Sniffer distributed architecture: Difference between revisions

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{{DISPLAYTITLE:Distributed Architecture: Client-Server Mode}}
{{DISPLAYTITLE:Distributed Architecture: Client-Server Mode}}


This guide explains how to deploy multiple VoIPmonitor sensors in a distributed architecture using the modern Client-Server mode.
This guide covers deploying multiple VoIPmonitor sensors in a distributed architecture using Client-Server mode (v20+).


== Overview ==
For deployment options including on-host vs dedicated sensors and traffic forwarding methods (SPAN, GRE, TZSP, VXLAN), see [[Sniffing_modes|VoIPmonitor Deployment & Topology Guide]].


VoIPmonitor v20+ uses a '''Client-Server architecture''' for distributed deployments. Remote sensors connect to a central server via encrypted TCP channel.
= Overview =
 
VoIPmonitor v20+ uses '''Client-Server architecture''' for distributed deployments. Remote sensors connect to a central server via encrypted TCP (default port 60024, zstd compression).


{| class="wikitable"
{| class="wikitable"
|-
|-
! Mode !! What is sent !! Processing location !! Use case
! Mode !! <code>packetbuffer_sender</code> !! What is Sent !! Processing Location !! Use Case
|-
|-
| '''Local Processing''' || CDRs only || Remote sensor || Multiple sites, low bandwidth
| '''Local Processing''' || <code>no</code> (default) || CDRs only || Remote sensor || Multi-site, low bandwidth
|-
|-
| '''Packet Mirroring''' || Raw packets || Central server || Centralized analysis, low-resource remotes
| '''Packet Mirroring''' || <code>yes</code> || Raw packets || Central server || Centralized analysis, low-resource remotes
|}
|}
The mode is controlled by a single option: <code>packetbuffer_sender</code>
For comprehensive deployment options including on-host vs dedicated sensors, traffic forwarding methods (SPAN, GRE, TZSP, VXLAN), and NFS/SSHFS alternatives, see [[Sniffing_modes|VoIPmonitor Deployment & Topology Guide]].
== Client-Server Mode ==
=== Architecture ===


<kroki lang="plantuml">
<kroki lang="plantuml">
Line 49: Line 43:
</kroki>
</kroki>


=== Configuration ===
== Use Cases ==
 
'''AWS VPC Traffic Mirroring Alternative:'''
If experiencing packet loss with AWS VPC Traffic Mirroring (VXLAN overhead, MTU fragmentation), use client-server mode instead:
* Install VoIPmonitor on each source EC2 instance
* Send via encrypted TCP to central server
* Eliminates VXLAN encapsulation and MTU issues
 
= Configuration =
 
== Remote Sensor (Client) ==


'''Remote Sensor (client):'''
<syntaxhighlight lang="ini">
<syntaxhighlight lang="ini">
id_sensor              = 2                    # unique per sensor
id_sensor              = 2                    # Unique per sensor (1-65535)
server_destination      = central.server.ip
server_destination      = central.server.ip
server_destination_port = 60024
server_destination_port = 60024
server_password        = your_strong_password
server_password        = your_strong_password


# Choose one:
# Choose mode:
packetbuffer_sender    = no    # Local Processing: analyze locally, send CDRs
packetbuffer_sender    = no    # Local Processing: analyze locally, send CDRs
# packetbuffer_sender  = yes    # Packet Mirroring: send raw packets
# packetbuffer_sender  = yes    # Packet Mirroring: send raw packets
Line 67: Line 70:
</syntaxhighlight>
</syntaxhighlight>


'''Important: Source IP Binding with <code>manager_ip</code>'''
{{Tip|1=For HA setups with floating IPs, use <code>manager_ip = 10.0.0.5</code> to bind outgoing connections to a static IP address.}}


For remote sensors with multiple IP addresses (e.g., in High Availability setups with a floating/virtual IP), use the <code>manager_ip</code> parameter to bind the outgoing connection to a specific static IP address. This ensures the central server sees a consistent source IP from each sensor, preventing connection issues during failover.
== Central Server ==


<syntaxhighlight lang="ini">
# On sensor with multiple interfaces (e.g., static IP + floating HA IP)
manager_ip              = 10.0.0.5    # Bind to the static IP address
server_destination      = 192.168.1.100
# The outgoing connection will use 10.0.0.5 as the source IP instead of the floating IP
</syntaxhighlight>
Useful scenarios:
* HA pairs: Sensors use static IPs while floating IP is only for failover management
* Multiple VNICs: Explicit source IP selection on systems with multiple virtual interfaces
* Network ACLs: Ensure connections originate from whitelisted IP addresses
'''Central Server:'''
<syntaxhighlight lang="ini">
<syntaxhighlight lang="ini">
server_bind            = 0.0.0.0
server_bind            = 0.0.0.0
Line 96: Line 86:
# If receiving raw packets (packetbuffer_sender=yes on clients):
# If receiving raw packets (packetbuffer_sender=yes on clients):
sipport                = 5060
sipport                = 5060
# ... other sniffer options
savertp                = yes
savesip                = yes
</syntaxhighlight>
</syntaxhighlight>


=== Custom Port Configuration ===
{{Warning|1='''Critical:''' Exclude <code>server_bind_port</code> from <code>sipport</code> on the central server. Including it causes continuously increasing memory usage.
 
'''Critical:''' The <code>server_bind_port</code> on the central server must match the <code>server_destination_port</code> on each remote sensor. If these ports do not match, sensors cannot connect.
 
<syntaxhighlight lang="ini">
<syntaxhighlight lang="ini">
# Central Server (listening on custom port 50291)
# WRONG - includes sensor communication port:
server_bind            = 0.0.0.0
sipport = 1-65535
server_bind_port        = 50291      # Custom port (default is 60024)
server_password        = your_strong_password
</syntaxhighlight>


<syntaxhighlight lang="ini">
# CORRECT - excludes port 60024:
# Remote Sensor (must match the server's custom port)
sipport = 1-60023,60025-65535
server_destination      = 45.249.9.2
</syntaxhighlight>}}
server_destination_port = 50291      # MUST match server_bind_port
server_password        = your_strong_password
</syntaxhighlight>


'''Common reasons to use a custom port:'''
== Key Configuration Rules ==


* Firewall restrictions that block the default port 60024
{| class="wikitable"
* Running multiple VoIPmonitor instances on the same server (each with a different port)
* Compliance requirements for non-standard ports
* Avoiding port conflicts with other services
 
''' Troubleshooting Connection Failures: '''
 
{| class="wikitable" style="background:#fff3cd; border:1px solid #ffc107;"
|-
|-
! colspan="2" style="background:#ffc107;" | Critical First Step: Check Traffic Rate Indicator
! Rule !! Applies To !! Why
|-
|-
| style="vertical-align: top;" | '''IMPORTANT:'''
| <code>server_bind_port</code> must match <code>server_destination_port</code> || Both || Connection fails if mismatched
| Before troubleshooting communication issues, check if the probe is receiving traffic. The traffic rate indicator in the sensor logs shows the current packet capture rate in the format <code>[x.xMb/s]</code> (e.g., <code>[12.5Mb/s]</code> or <code>[0.0Mb/s]</code>).
|-
|-
| style="vertical-align: top;" | '''How to check:'''
| <code>sipport</code> must match on probe and central server || Packet Mirroring || Missing ports = missing calls
| Run <code>journalctl -u voipmonitor -n 100</code> on the probe and look for the traffic rate indicator printed in the status logs.
|-
|-
| style="vertical-align: top;" | '''If showing <code>[0.0Mb/s]</code>:'''
| <code>natalias</code> only on central server || Packet Mirroring || Prevents RTP correlation issues
| The issue is NOT communication or authentication. The problem is network configuration on the probe side. Common causes: incorrect SPAN/mirror port setup on the switch, wrong network interface selected in <code>voipmonitor.conf</code>, or the probe is not receiving any traffic at all. Fix the network configuration first.
|-
|-
| style="vertical-align: top;" | '''If showing traffic (non-zero rate):'''
| Each sensor needs unique <code>id_sensor</code> || All || Required for identification
| The probe IS receiving traffic from the network, so the handshake issue is with communication/authentication. Proceed with the steps below.
|}
|}


If probes cannot connect to the server and the traffic rate indicator shows non-zero traffic:
= Local Processing vs Packet Mirroring =
 
1. '''Verify ports match on both sides:'''
  <syntaxhighlight lang="bash">
  # On central server - check which port it is listening on
  ss -tulpn | grep voipmonitor
  # Should show: voipmonitor LISTEN 0.0.0.0:50291
  </syntaxhighlight>
 
2. '''Test connectivity from remote sensor:'''
  <syntaxhighlight lang="bash">
  # Test TCP connection to the server's custom port
  nc -zv 45.249.9.2 50291
  # Success: "Connection to 45.249.9.2 50291 port [tcp/*] succeeded!"
  # Timeout/Refused: Check firewall or misconfigured port
  </syntaxhighlight>
 
3. '''Ensure firewall allows the custom port:'''
  <syntaxhighlight lang="bash">
  # Allow inbound TCP on custom port (example for firewalld)
  firewall-cmd --permanent --add-port=50291/tcp
  firewall-cmd --reload
  </syntaxhighlight>
 
4. '''Check logs on both sides:'''
  <syntaxhighlight lang="bash">
  journalctl -u voipmonitor -f
  # Look for: "connecting to server", "connection refused", or "timeout"
  </syntaxhighlight>
 
5. '''Verify MySQL database is accessible (if web GUI works but sensors cannot connect):'''
  If the web portal is accessible but sensors cannot connect, verify that the MySQL/MariaDB database service on the primary server is running and responsive. The central VoIPmonitor service requires a functioning database connection to accept sensor data.
  <syntaxhighlight lang="bash">
  # Check if MySQL service is running
  systemctl status mariadb
  # or
  systemctl status mysqld
 
  # Check for database errors in MySQL error log
  # Common locations:
  tail -50 /var/log/mariadb/mariadb.log
  tail -50 /var/log/mysql/error.log
  # Look for critical errors that might prevent database connections
  </syntaxhighlight>
 
If MySQL is down or experiencing critical errors, the central VoIPmonitor server may not be able to accept sensor connections even though the web interface (PHP) remains accessible. Restart the database service if needed and monitor the logs for recurring errors.
 
After changing port configuration, restart the service:
 
<syntaxhighlight lang="bash">
systemctl restart voipmonitor
</syntaxhighlight>
 
=== Checking Sensor Health Status via Management API ===
 
Each VoIPmonitor sensor exposes a TCP management API (default port 5029) that can be used to query its operational status and health. This is useful for monitoring multiple sensors, especially in distributed deployments.
 
'''Important Notes:'''
* There is NO single command to check all sensors simultaneously
* Each sensor must be queried individually
* The `sniffer_stat` command returns JSON with sensor status information
* In newer VoIPmonitor versions, the sensor's management API communication may be encrypted
 
==== Basic Health Check Command ====
 
To check the status of a single sensor:
 
<syntaxhighlight lang="bash">
# Query sensor status via management port
echo 'sniffer_stat' | nc <sensor_ip> <sensor_port>
</syntaxhighlight>
 
Replace:
* <code>&lt;sensor_ip&gt;</code> with the IP address of the sensor
* <code>&lt;sensor_port&gt;</code> with the management port (default: 5029)
 
==== Example Response ====
 
The command returns a JSON object with sensor status information:
 
<pre>
{
  "status": "running",
  "version": "30.3-SVN.123",
  "uptime": 86400,
  "calls_active": 42,
  "calls_total": 12345,
  "packets_per_second": 1250.5,
  "packets_dropped": 0
}
</pre>
 
==== Scripting Multiple Sensors ====
 
To check multiple sensors and get a consolidated result, create a script that queries each sensor individually:
 
<syntaxhighlight lang="bash">
#!/bin/bash
# Check health of multiple sensors
 
SENSORS=("192.168.1.10:5029" "192.168.1.11:5029" "192.168.1.12:5029")
ALL_OK=true
 
for SENSOR in "${SENSORS[@]}"; do
    IP=$(echo $SENSOR | cut -d: -f1)
    PORT=$(echo $SENSOR | cut -d: -f2)
 
    echo -n "Checking $IP:$PORT ... "
 
    # Query sensor and check for running status
    STATUS=$(echo 'sniffer_stat' | nc -w 2 $IP $PORT 2>/dev/null | grep -o '"status":"[^"]*"' | cut -d'"' -f4)
 
    if [ "$STATUS" = "running" ]; then
        echo "OK"
    else
        echo "FAILED (status: $STATUS)"
        ALL_OK=false
    fi
done
 
if [ "$ALL_OK" = true ]; then
    echo "All sensors healthy"
    exit 0
else
    echo "One or more sensors unhealthy"
    exit 1
fi
</syntaxhighlight>
 
==== Troubleshooting Management API Access ====
 
If you cannot connect to the sensor management API:
 
1. '''Verify the management port is listening:'''
  <syntaxhighlight lang="bash">
  # On the sensor host
  netstat -tlnp | grep 5029
  # or
  ss -tlnp | grep voipmonitor
  </syntaxhighlight>
 
2. '''Check firewall rules:'''
  Ensure TCP port 5029 is allowed from the monitoring host to the sensor.
 
3. '''Test connectivity with netcat:'''
  <syntaxhighlight lang="bash">
  nc -zv <sensor_ip> 5029
  </syntaxhighlight>
 
4. '''Encrypted Communication (Newer Versions):'''
  In newer VoIPmonitor versions, the sensor's API communication may be encrypted. If management API access fails with encryption errors:
  * Check VoIPmonitor documentation for your version
  * Encryption may need to be disabled for management API access
  * Consult support for encrypted CLI tools if available
 
==== Encryption Considerations ====
 
If your sensors use encrypted management API (newer versions):
 
* The standard netcat command may not work with encrypted connections
* Check if `manager_bind` (default port 5029) has encryption enabled
* For encrypted connections, you may need VoIPmonitor-specific CLI tools
* Refer to your VoIPmonitor version documentation or contact support for encrypted API access
 
=== Connection Compression ===
 
The client-server channel supports compression to reduce bandwidth usage:
 
<syntaxhighlight lang="ini">
# On both client and server (default: zstd)
server_type_compress = zstd
</syntaxhighlight>
 
Available options: <code>zstd</code> (default, recommended), <code>gzip</code>, <code>lzo</code>, <code>none</code>
 
=== High Availability (Failover) ===
 
Remote sensors can specify multiple central server IPs for automatic failover:
 
<syntaxhighlight lang="ini">
# Remote sensor configuration with failover
server_destination = 192.168.0.1, 192.168.0.2
</syntaxhighlight>
 
If the primary server becomes unavailable, the sensor automatically connects to the next server in the list.
 
== Local Processing vs Packet Mirroring ==


{| class="wikitable"
{| class="wikitable"
Line 337: Line 122:
| '''<code>packetbuffer_sender</code>''' || <code>no</code> (default) || <code>yes</code>
| '''<code>packetbuffer_sender</code>''' || <code>no</code> (default) || <code>yes</code>
|-
|-
| '''Packet analysis''' || On remote sensor || On central server
| '''Processing location''' || Remote sensor || Central server
|-
|-
| '''PCAP storage''' || On remote sensor || On central server
| '''PCAP storage''' || Remote sensor || Central server
|-
|-
| '''WAN bandwidth''' || Low (CDRs only) || High (full packets)
| '''WAN bandwidth''' || Low (CDRs only, 1Gb sufficient) || High (full packets)
|-
|-
| '''Remote CPU load''' || Higher || Minimal
| '''Remote CPU load''' || Higher || Minimal
|-
|-
| '''Use case''' || Standard multi-site || Low-resource remotes
| '''Capture rules applied''' || On sensor || On central server only
|}
 
=== Network Bandwidth Requirements ===
 
The network bandwidth requirements between remote sensors and the central server depend on the selected operational mode:
 
{| class="wikitable" style="background:#e8f4f8; border:1px solid #4A90E2;"
|-
! colspan="2" style="background:#4A90E2; color: white;" | Bandwidth Guidelines
|-
| style="vertical-align: top;" | '''Local Processing Mode (<code>packetbuffer_sender=no</code>):'''
| PCAP files are stored locally on sensors. Network traffic consists mainly of CDR data (SQL queries). <br><br>
'''A 1Gb network connection between sensors and the central GUI/Database server is generally sufficient for most deployments.'''
|-
| style="vertical-align: top;" | '''Packet Mirroring Mode (<code>packetbuffer_sender=yes</code>):'''
| Raw packet stream is forwarded to central server. Bandwidth consumption is roughly equivalent to the VoIP traffic volume itself (minus Ethernet headers, plus compression overhead). <br><br>
Consider your expected VoIP traffic volume and network capacity. Use <code>server_type_compress=zstd</code> to reduce bandwidth usage.
|}
|}


For optimal throughput in high-latency environments, see the server concatenation limit configuration in [[Sniffer_configuration#SQL_Concatenation_Throughput_Tuning|Sniffer Configuration: SQL Concatenation Throughput]].
== PCAP Access in Local Processing Mode ==


=== PCAP Access in Local Processing Mode ===
PCAPs are stored on remote sensors. The GUI retrieves them through the central server, which proxies the request to the sensor '''over the existing TCP/60024 connection''' - the same persistent encrypted channel the sensor uses for sending CDRs. This connection is bidirectional; the central server does not open any separate connection back to the sensor.
 
When using Local Processing, PCAPs are stored on remote sensors. The GUI retrieves them via the central server, which proxies requests to each sensor's management port (TCP/5029).


'''Firewall requirements:'''
'''Firewall requirements:'''
* Central server must reach remote sensors on TCP/5029
* Remote sensors must reach central server on TCP/60024
== Dashboard Statistics ==
Dashboard widgets (SIP/RTP/REGISTER counts) depend on where packet processing occurs:


{| class="wikitable"
{| class="wikitable"
|-
|-
! Configuration !! Where statistics appear
! Direction !! Port !! Purpose
|-
|-
| '''<code>packetbuffer_sender = yes</code>''' (Packet Mirroring) || Central server only
| Remote sensors → Central server || TCP/60024 || Persistent encrypted channel (CDRs from sensor, PCAP requests from server - bidirectional)
|-
|-
| '''<code>packetbuffer_sender = no</code>''' (Local Processing) || Both sensor and central server
| GUI → Central server || TCP/5029 || Manager API (sensor status, active calls, configuration)
|-
| GUI → Central server || TCP/60024 || Server API (list connected sensors, proxy PCAP retrieval)
|}
|}


'''Note:''' If you are using Packet Mirroring mode (<code>packetbuffer_sender=yes</code>) and see empty dashboard widgets for the forwarding sensor, this is expected behavior. The sender sensor only captures and forwards raw packets - it does not create database records or statistics. The central server performs all processing.
{{Note|1=The central server does '''not''' initiate connections to remote sensors. All server↔sensor communication happens over the single TCP/60024 connection that the sensor established.}}


=== Enabling Local Statistics on Forwarding Sensors ===
{{Tip|1=Packet Mirroring (<code>packetbuffer_sender=yes</code>) '''automatically deduplicates calls''' - the central server merges packets from all probes for the same Call-ID into a single unified CDR. This also ensures one logical call only consumes one license channel.}}
= Advanced Topics =


If you need local statistics on a sensor that was previously configured to forward packets:
== High Availability (Failover) ==
 
Remote sensors can specify multiple central servers:


<syntaxhighlight lang="ini">
<syntaxhighlight lang="ini">
# On the forwarding sensor
server_destination = 192.168.0.1, 192.168.0.2
packetbuffer_sender = no
</syntaxhighlight>
</syntaxhighlight>


This disables packet forwarding and enables full local processing. Note that this increases CPU and RAM usage on the sensor since it must perform full SIP/RTP analysis.
If primary is unavailable, the sensor automatically connects to the next server.
 
== Controlling Packet Storage in Packet Mirroring Mode ==


When using Packet Mirroring (<code>packetbuffer_sender=yes</code>), the central server processes raw packets received from sensors. The <code>save*</code> options on the '''central server''' control which packets are saved to disk.
== Connection Compression ==


<syntaxhighlight lang="ini">
<syntaxhighlight lang="ini">
# Central Server Configuration (receiving raw packets from sensors)
# On both client and server (default: zstd)
server_bind            = 0.0.0.0
server_type_compress = zstd  # Options: zstd, gzip, lzo, none
server_bind_port        = 60024
server_password        = your_strong_password
 
# Database Configuration
mysqlhost              = localhost
mysqldb                = voipmonitor
mysqluser              = voipmonitor
mysqlpassword          = db_password
 
# Sniffer options needed when receiving raw packets:
sipport                = 5060
 
# CONTROL PACKET STORAGE HERE:
# These settings on the central server determine what gets saved:
savertp                = yes          # Save RTP packets
savesip                = yes          # Save SIP packets
saveaudio              = wav          # Export audio recordings (optional)
</syntaxhighlight>
</syntaxhighlight>


{| class="wikitable" style="background:#e8f4f8; border:1px solid #4A90E2;"
== Intermediate Server (Hub-and-Spoke) ==
|-
! colspan="2" style="background:#4A90E2; color: white;" | Important: Central Server Controls Storage
|-
| style="vertical-align: top;" | '''Key Point:'''
| When sensors send raw packets to a central server, the storage is controlled by the <code>savertp</code>, <code>savesip</code>, and <code>saveaudio</code> options configured on the '''central server''', not on the individual sensors. The sensors are only forwarding raw packets - they do not make decisions about what to save unless you are using Local Processing mode.
|}


This centralized control allows you to:
An intermediate server can receive from multiple sensors and forward to a central server:
* Enable/disable packet types (RTP, SIP, audio) from one location
* Adjust storage settings without touching each sensor
* Apply capture rules from the central server to filter traffic


== Data Storage Summary ==
<kroki lang="plantuml">
@startuml
skinparam shadowing false
skinparam defaultFontName Arial


* '''CDRs''': Always stored in MySQL on central server
rectangle "Remote Sensors" as RS
* '''PCAPs''':
rectangle "Intermediate Server" as INT
** Local Processing → stored on each remote sensor
rectangle "Central Server" as CS
** Packet Mirroring → stored on central server
database "MySQL" as DB


== Handling Same Call-ID from Multiple Sensors ==
RS --> INT : TCP/60024
 
INT --> CS : TCP/60024
When a call passes through multiple sensors that see the same SIP Call-ID, VoIPmonitor automatically merges the SIP packets into a single CDR on the central server. This is expected behavior when using Packet Mirroring mode.
CS --> DB
 
@enduml
{| class="wikitable" style="background:#fff3cd; border:1px solid #ffc107;"
</kroki>
|-
! colspan="2" style="background:#ffc107;" | Call-ID Merging Behavior
|-
| style="vertical-align: top;" | '''What happens:'''
| If Sensor A and Sensor B both forward packets for a call with the same Call-ID to the central server, VoIPmonitor creates a single CDR containing SIP packets from both sensors. The RTP packets are captured from whichever sensor processed the media.
|-
| style="vertical-align: top;" | '''Why:'''
| VoIPmonitor uses the SIP Call-ID as the primary unique identifier. When multiple sensors forward packets with the same Call-ID to a central server, they are automatically treated as one call.
|-
| style="vertical-align: top;" | '''Is it a problem?'''
| Usually not. For most deployments, combining records from multiple sensors for the same call (different call legs passing through different points in the network) is the desired behavior.
|}
 
=== Preventing Duplicate CDRs in Local Processing Mode ===
 
When using '''Local Processing mode''' (<code>packetbuffer_sender=no</code>), each remote probe processes its own packets and writes CDRs directly to a central database. If multiple probes capture the same call (e.g., redundant taps or overlapping SPAN ports), this creates '''duplicate CDR entries''' in the database.
 
To prevent duplicates in this scenario, use the <code>cdr_check_exists_callid</code> option on '''all probes''':
 
{| class="wikitable" style="background:#f8f9fa; border:1px solid #dee2e6;"
|-
! rowspan="2" | Setting
! colspan="2" | Result
|-
|<code>cdr_check_exists_callid = no</code> (default)
|Each probe creates its own CDR row. Multiple probes capturing the same call result in duplicate entries with the same Call-ID but different id_sensor values.
|-
|<code>cdr_check_exists_callid = yes</code>
|Probes check for an existing CDR with the same Call-ID before inserting. If found, they update the existing row instead of creating a new one. The final CDR will be associated with the id_sensor of the probe that last processed the call.
|}
 
'''Prerequisites:'''
* MySQL user must have <code>UPDATE</code> privileges on the <code>cdr</code> table
* All probes must be configured with this setting


<syntaxhighlight lang="ini">
<syntaxhighlight lang="ini">
# Add to voipmonitor.conf on each probe (Local Processing mode only)
# On INTERMEDIATE SERVER
[general]
id_sensor              = 100
cdr_check_exists_callid = yes
</syntaxhighlight>
 
'''Note:''' This setting is only useful in Local Processing mode. In Packet Mirroring mode (<code>packetbuffer_sender=yes</code>), the central server automatically merges packets with the same Call-ID, so this option is not needed.
 
=== Keeping Records Separate Per Sensor ===
 
If you need to keep records completely separate when multiple sensors see the same Call-ID (e.g., each sensor should create its own independent CDR even for calls with overlapping Call-IDs), you must run '''multiple receiver instances on the central server'''.


<syntaxhighlight lang="ini">
# Receive from remote sensors
# Receiver Instance 1 (for Sensor A)
[receiver_sensor_a]
server_bind            = 0.0.0.0
server_bind            = 0.0.0.0
server_bind_port        = 60024
server_bind_port        = 60024
mysqlhost              = localhost
server_password        = sensor_password
mysqldb                = voipmonitor
 
mysqluser              = voipmonitor
# Forward to central server
mysqlpassword          = <password>
server_destination      = central.server.ip
mysqltableprefix        = sensor_a_  # Separate CDR tables
server_destination_port = 60024
id_sensor              = 2
# ... other options


# Receiver Instance 2 (for Sensor B)
packetbuffer_sender    = no    # or yes, depending on desired mode
[receiver_sensor_b]
server_bind            = 0.0.0.0
server_bind_port        = 60025  # Different port
mysqlhost              = localhost
mysqldb                = voipmonitor
mysqluser              = voipmonitor
mysqlpassword          = <password>
mysqltableprefix        = sensor_b_  # Separate CDR tables
id_sensor              = 3
# ... other options
</syntaxhighlight>
</syntaxhighlight>


Each receiver instance runs as a separate process, listens on a different port, and can write to separate database tables (using <code>mysqltableprefix</code>). Configure each sensor to connect to its dedicated receiver port.
{{Note|1=This works because the intermediate server does NOT do local packet capture - it only relays. Original remote sensors must be manually added to GUI Settings for visibility.}}
 
For more details on correlating multiple call legs from the same call, see [[Merging_or_correlating_multiple_call_legs]].
 
== GUI Visibility ==
 
Remote sensors appear automatically when connected. To customize names or configure additional settings:
# Go to '''GUI → Settings → Sensors'''
# Sensors are identified by their <code>id_sensor</code> value
 
== Troubleshooting Distributed Deployments ==
 
=== Probe Not Detecting All Calls on Expected Ports ===


If a remote sensor (probe) configured for packet mirroring is not detecting all calls on expected ports, check configuration on '''both''' the probe and the central analysis host.
== Multiple Receivers for Packet Mirroring ==


{| class="wikitable" style="background:#fff3cd; border:1px solid #ffc107;"
{{Warning|1=Multiple sensors with <code>packetbuffer_sender=yes</code> sending to a '''single receiver instance''' can cause call processing conflicts (calls appear in Active Calls but missing from CDRs).}}
|-
! colspan="2" style="background:#ffc107;" | Critical: sipport Must Match in Distributed Deployments
|-
| style="vertical-align: top;" | '''The Issue:'''
| In distributed/probe setups using Packet Mirroring (<code>packetbuffer_sender=yes</code>), calls will be missing if the <code>sipport</code> configuration is not aligned between the probe and central server. Common symptom: Probe sees traffic via <code>tcpdump</code> but central server records incomplete CDRs.
|-
| style="vertical-align: top;" | '''Configuration Requirement:'''
| The probe and central host must have consistent <code>sipport</code> values. If your network uses SIP on multiple ports (e.g., 5060, 5061, 5080, 6060), ALL ports must be listed on both systems.
|}


The solution involves three steps:
'''Solution:''' Run separate receiver instances on different hosts, each dedicated to specific sensors:


;1. Verify traffic reachability on the probe:
Use <code>tcpdump</code> on the probe VM to confirm SIP packets for the missing calls are arriving on the expected ports.
<pre>
# On the probe VM
tcpdump -i eth0 -n port 5060
</pre>
;2. Check the probe's ''voipmonitor.conf'':
Ensure the <code>sipport</code> directive on the probe includes all necessary SIP ports used in your network.
<syntaxhighlight lang="ini">
<syntaxhighlight lang="ini">
# /etc/voipmonitor.conf on the PROBE
# Receiver Instance 1 (Host 1, for Sensor A)
sipport = 5060,5061,5080,6060
server_bind_port        = 60024
</syntaxhighlight>
id_sensor              = 1


;3. Check the central analysis host's ''voipmonitor.conf'':
# Receiver Instance 2 (Host 2, for Sensor B)
'''This is the most common cause of missing calls in distributed setups.''' The central analysis host (specified by <code>server_bind</code> on the central server, or by <code>server_destination</code> configured on the probe) must also have the <code>sipport</code> directive configured with the same list of ports used by all probes.
server_bind_port        = 60024
<syntaxhighlight lang="ini">
id_sensor              = 2
# /etc/voipmonitor.conf on the CENTRAL HOST
sipport = 5060,5061,5080,6060
</syntaxhighlight>
</syntaxhighlight>


;4. Restart both services:
Alternative: Use '''Local Processing mode''' (<code>packetbuffer_sender=no</code>) which processes calls independently on each sensor.
Apply the configuration changes:
<syntaxhighlight lang="bash">
# On both probe and central host
systemctl restart voipmonitor
</syntaxhighlight>


{| class="wikitable" style="background:#e8f4f8; border:1px solid #4A90E2;"
== Preventing Duplicate CDRs (Local Processing) ==
|-
! colspan="2" style="background:#4A90E2; color: white;" | Why Both Systems Must Match
|-
| style="vertical-align: top;" | '''Probe side:'''
| The probe captures packets from the network interface. Its <code>sipport</code> setting determines which UDP ports it considers as SIP traffic to capture and forward.
|-
| style="vertical-align: top;" | '''Central server side:'''
| When receiving raw packets in Packet Mirroring mode, the central server analyzes the packets locally. Its <code>sipport</code> setting determines which ports it interprets as SIP during analysis. If a port is missing here, packets are captured but not recognized as SIP, resulting in missing CDRs.
|}


=== Quick Diagnosis Commands ===
When multiple probes capture the same call in Local Processing mode:


On the probe:
<syntaxhighlight lang="ini">
<syntaxhighlight lang="bash">
# On each probe
# Check which sipport values are configured
cdr_check_exists_callid = yes
grep -E "^sipport" /etc/voipmonitor.conf
 
# Verify traffic is arriving on expected ports
tcpdump -i eth0 -nn -c 10 port 5061
</syntaxhighlight>
</syntaxhighlight>


On the central server:
This checks for existing CDRs before inserting. Requires MySQL UPDATE privileges.
<syntaxhighlight lang="bash">
# Check which sipport values are configured
grep -E "^sipport" /etc/voipmonitor.conf
 
# Check syslog for analysis activity (should see processing packets)
tail -f /var/log/syslog | grep voipmonitor
</syntaxhighlight>


If probes still miss calls after ensuring <code>sipport</code> matches on both sides, check the [[Sniffer_troubleshooting|full troubleshooting guide]] for other potential issues such as network connectivity, firewall rules, or interface misconfiguration.
== Critical: SIP and RTP Must Be Captured Together ==


=== RTP Streams End Prematurely in Distributed Deployments ===
VoIPmonitor cannot correlate SIP and RTP from different sniffer instances. A '''single sniffer must process both SIP and RTP''' for each call. Parameters like <code>cdr_check_exists_callid</code> do NOT enable split SIP/RTP correlation.


If RTP streams end prematurely in call recordings when using a remote sniffer with a central GUI, this is often caused by the <code>natalias</code> configuration being set on the wrong system.


'''The Problem:'''


When packets are forwarded from a remote sniffer to a central server (Packet Mirroring mode), the central server sees the packets with their original IP addresses as captured by the sniffer. If <code>natalias</code> is configured on the remote sniffer, the IP address substitution happens at capture time. This can cause the central server's RTP correlation logic to fail because the substituted addresses do not match what the central server sees in the SIP signaling.
==== Split SIP/RTP with Packet Mirroring Mode ====


'''The Solution:'''
{{Note|1='''Exception for Packet Mirroring Mode:''': The above limitation applies to '''Local Processing mode''' (<code>packetbuffer_sender=no</code>) where each sensor processes calls independently. In '''Packet Mirroring mode''' (<code>packetbuffer_sender=yes</code>), the central server receives raw packets from multiple remote sensors and processes them together. This allows scenarios where SIP and RTP are captured on separate nodes - configure both as packet senders and let the central server correlate them into single unified CDRs.}}
 
Configure <code>natalias</code> only on the central server that receives and processes the packets, not on the remote sniffer that captures and forwards them.
 
{| class="wikitable" style="background:#fff3cd; border:1px solid #ffc107;"
|-
! colspan="2" style="background:#ffc107;" | Critical: natalias Configuration Placement
|-
| style="vertical-align: top;" | '''Remote Sniffer (packet forwarding):'''
| Do NOT set <code>natalias</code> on the remote sensor. Let it forward packets with their original IP addresses.
|-
| style="vertical-align: top;" | '''Central Server (packet processing):'''
| Configure <code>natalias</code> on the central server that performs the analysis. The address substitution happens during correlation, at the point where SIP and RTP are matched.
|}
 
'''Configuration Example:'''


Example scenario: Separate SIP signaling node and RTP handling node:
<syntaxhighlight lang="ini">
<syntaxhighlight lang="ini">
# WRONG: Do NOT configure natalias on remote sniffer
# SIP Signaling Node (packet sender)
# /etc/voipmonitor.conf on REMOTE SENSOR
id_sensor              = 1
# natalias = 1.2.3.4 10.0.0.5  # DON'T DO THIS
packetbuffer_sender    = yes
server_destination      = central.server.ip
server_destination_port = 60024
server_password        = your_password


# CORRECT: Configure natalias on central server
# RTP Handling Node (packet sender)
# /etc/voipmonitor.conf on CENTRAL SERVER
id_sensor              = 2
natalias = 1.2.3.4 10.0.0.5
packetbuffer_sender    = yes
server_bind = 0.0.0.0
server_destination      = central.server.ip
server_bind_port = 60024
server_destination_port = 60024
# ... other central server settings
server_password        = your_password
</syntaxhighlight>
</syntaxhighlight>


'''After Changing Configuration:'''
The central server merges packets from both senders by Call-ID, creating unified CDRs with complete SIP and RTP data.


<syntaxhighlight lang="bash">
# Restart voipmonitor on BOTH systems
systemctl restart voipmonitor
</syntaxhighlight>


This ensures that RTP packets are correctly associated with their SIP dialogs on the central server, even when the network traverses NAT devices.
==== HEP Protocol in Client/Server Mode ====


== Legacy: Mirror Mode ==
VoIPmonitor supports receiving HEP-encapsulated traffic on sniffer clients and forwarding it to a central server. This enables distributed capture from HEP sources (Kamailio, OpenSIPS, rtpproxy, FreeSWITCH) in a client/server architecture.


'''Note:''' The older <code>mirror_destination</code>/<code>mirror_bind</code> options still exist but the modern Client-Server approach with <code>packetbuffer_sender=yes</code> is preferred as it provides encryption and simpler management.
'''Scenario:''' SIP proxy and RTP proxy at different locations sending HEP to remote sniffer clients:


=== Debugging SIP Traffic in Distributed Architecture ===
<syntaxhighlight lang="ini">
# Remote Sniffer Client A (receives HEP from Kamailio)
id_sensor              = 1
hep                    = yes
hep_bind_port          = 9060
packetbuffer_sender    = yes
server_destination      = central.server.ip
server_destination_port = 60024
server_password        = your_password


When using the Client-Server architecture (Packet Mirroring or Local Processing), standard packet capture tools like <code>sngrep</code> cannot see SIP packets on the central server because the traffic is encapsulated inside the encrypted TCP tunnel between the sensor and the central server.
# Remote Sniffer Client B (receives HEP from rtpproxy)
id_sensor              = 2
hep                    = yes
hep_bind_port          = 9060
packetbuffer_sender    = yes
server_destination      = central.server.ip
server_destination_port = 60024
server_password        = your_password
</syntaxhighlight>


{| class="wikitable" style="background:#e8f4f8; border:1px solid #4A90E2;"
The central server receives packets from both clients and correlates them into unified CDRs using standard SIP Call-ID and IP:port from SDP.
|-
! colspan="2" style="background:#4A90E2; color: white;" | Why sngrep Does Not Work on Central Server
|-
| style="vertical-align: top;" | '''The Issue:'''
| <code>sngrep</code> relies on capturing raw SIP packets directly from the network interface. In Client-Server mode, remote sensors forward traffic to the central server inside an encrypted TCP channel (default port 60024 with zstd compression). The SIP packets are wrapped inside this tunnel and cannot be inspected by standard tools.
|-
| style="vertical-align: top;" | '''What You See:'''
| <code>tcpdump</code> on the central server shows encrypted TCP packets on port 60024 (Packet Mirroring) or SQL traffic on port 3306 (Local Processing). No raw SIP packets (UDP 5060) are visible on the wire.
|}


To inspect SIP packets in distributed deployments, use one of these methods:
{{Note|1=This also works for IPFIX (Oracle SBCs) and RibbonSBC protocols forwarded via client/server mode.}}


==== Live Sniffer (Recommended) ====
'''Alternative: Direct HEP to single sniffer'''


The '''Live Sniffer''' feature in the VoIPmonitor GUI provides real-time SIP packet display from remote sensors. This is the preferred method for debugging call flows and network issues in distributed architectures.
If both HEP sources can reach the same sniffer directly, no client/server setup is needed:


<syntaxhighlight lang="bash">
<syntaxhighlight lang="ini">
# To use Live Sniffer:
# Single sniffer receiving HEP from multiple sources
# 1. Open the VoIPmonitor GUI
hep                    = yes
# 2. Navigate to "Live Sniffer"
hep_bind_port          = 9060
# 3. Select the remote sensor from the dropdown
interface              = eth0  # Can also sniff locally if needed
# 4. Click "Start" to view live SIP packets from that sensor
</syntaxhighlight>
</syntaxhighlight>


The Live Sniffer streams SIP packets from the sensor to the GUI in real-time via the Manager API (TCP port 5029). Features include:
Both Kamailio (SIP) and rtpproxy (RTP) send HEP to this sniffer on port 9060. The sniffer correlates them automatically based on Call-ID and SDP IP:port.
* Call coloring by Call-ID
= Sensor Health Monitoring =
* Packet details inspection
* Call flow visualization
* Multi-user support


For setup and troubleshooting of Live Sniffer, see [[Live_sniffer|Live Sniffer documentation]].
== Management API ==


==== sngrep on Remote Sensors ====
Query sensor status via TCP port 5029:
 
If you need to use <code>sngrep</code> directly, run it on the **remote sensor machine** where the traffic first arrives from the network interface before VoIPmonitor encapsulation occurs.


<syntaxhighlight lang="bash">
<syntaxhighlight lang="bash">
# SSH into the remote sensor
echo 'sniffer_stat' | nc <sensor_ip> 5029
# Run sngrep on the interface connected to the SPAN/mirror port
sngrep -i eth0
</syntaxhighlight>
</syntaxhighlight>


Replace <code>eth0</code> with the actual network interface on the sensor that receives the mirrored traffic from the switch.
Returns JSON with status, version, active calls, packets per second, etc.
 
==== Verify Connectivity on Central Server ====


If you need to verify that data is flowing from sensors to the central server:
== Multi-Sensor Health Check Script ==


<syntaxhighlight lang="bash">
<syntaxhighlight lang="bash">
# Check for encrypted tunnel traffic (Packet Mirroring mode)
#!/bin/bash
tcpdump -i any port 60024
SENSORS=("192.168.1.10:5029" "192.168.1.11:5029")
 
for SENSOR in "${SENSORS[@]}"; do
# Check for SQL traffic (Local Processing mode)
    IP=$(echo $SENSOR | cut -d: -f1)
tcpdump -i any port 3306
    PORT=$(echo $SENSOR | cut -d: -f2)
 
    STATUS=$(echo 'sniffer_stat' | nc -w 2 $IP $PORT 2>/dev/null | grep -o '"status":"[^"]*"' | cut -d'"' -f4)
# Check sensor statistics via Management API
    echo "$IP: ${STATUS:-FAILED}"
echo 'sniffer_stat' | nc <sensor_ip> 5029
done
</syntaxhighlight>
</syntaxhighlight>


=== Migrating from Mirror Mode to Client-Server Mode ===
= Version Compatibility =


If your system uses the legacy mirror mode (<code>mirror_destination</code> on probes, <code>mirror_bind</code> on server), you should migrate to the modern client/server mode. Common symptoms of mirror mode issues include all CDRs being incorrectly associated with a single sensor after system updates.
{| class="wikitable"
 
{| class="wikitable" style="background:#fff3cd; border:1px solid #ffc107;"
|-
|-
! colspan="2" style="background:#ffc107;" | Why Migration is Recommended
! Scenario !! Compatibility !! Notes
|-
|-
| style="vertical-align: top;" | '''Mirror Mode Limitations:'''
| '''GUI ≥ Sniffer''' || ✅ Compatible || Recommended
| * No encryption (raw UDP traffic)
* Complex firewall configuration (must open mirroring port)
* Less robust connection handling
* Configuration can be lost during OS upgrades
|-
|-
| style="vertical-align: top;" | '''Client-Server Advantages:'''
| '''GUI < Sniffer''' || ⚠️ Risk || Sensor may write to non-existent columns
| * Encrypted TCP connections
* Automatic reconnection with failover
* Centralized port configuration
* Better troubleshooting capabilities
|}
|}


==== Prerequisites
'''Best practice:''' Upgrade GUI first (applies schema changes), then upgrade sensors.


* Central server hostname or IP address
For mixed versions temporarily, add to central server:
* Port for client-server communication (default: 60024)
* Strong shared password for authentication
 
==== Migration Steps
 
;1. Stop the voipmonitor sniffer service on all probe machines:
<syntaxhighlight lang="bash">
# On each probe
systemctl stop voipmonitor
</syntaxhighlight>
 
;2. Update GUI Sensors list:
# Log in to the VoIPmonitor GUI
# Navigate to '''Settings → Sensors'''
# Remove all old probe records, keeping only the server instance (e.g., localhost or the central server IP)
 
;3. Configure the Central Server:
Edit <code>/etc/voipmonitor.conf</code> on the central server:
<syntaxhighlight lang="ini">
<syntaxhighlight lang="ini">
# COMMENT OUT or remove mirror mode parameters:
server_cp_store_simple_connect_response = yes  # Sniffer 2024.11.0+
# mirror_bind_ip = 1.2.3.4
# mirror_bind_port = 9000
 
# ADD client-server mode parameters:
server_bind              = <server_ip>    # Use 0.0.0.0 to listen on all interfaces
server_bind_port        = <port>          # Default is 60024
server_password          = <a_strong_password>
 
# MySQL configuration remains unchanged
mysqlhost                = localhost
mysqldb                  = voipmonitor
mysqluser                = voipmonitor
mysqlpassword            = <your_db_password>
</syntaxhighlight>
</syntaxhighlight>


Restart the service on the central server:
= Troubleshooting =
<syntaxhighlight lang="bash">
# On central server
systemctl restart voipmonitor
</syntaxhighlight>


Verify the server is listening:
== Quick Diagnosis ==
<syntaxhighlight lang="bash">
# Check that voipmonitor is listening on the configured port
ss -tulpn | grep voipmonitor
# Should show: voipmonitor LISTEN 0.0.0.0:60024 (or your custom port)
</syntaxhighlight>


;4. Configure each Probe:
{| class="wikitable"
Edit <code>/etc/voipmonitor.conf</code> on each remote probe:
|-
<syntaxhighlight lang="ini">
! Symptom !! First Check !! Likely Cause
# COMMENT OUT or remove mirror mode parameters:
# mirror_destination_ip = 1.2.3.4
# mirror_destination_port = 9000
 
# ADD client-server mode parameters:
id_sensor                = <unique_id>    # Must be unique per sensor
server_destination      = <server_ip>
server_destination_port  = <port>          # Must match server_bind_port
server_password          = <a_strong_password>  # Same password used on server
 
# IMPORTANT: Set packet handling mode
packetbuffer_sender      = no    # Local Processing: analyze locally, send CDRs only
# OR
# packetbuffer_sender    = yes  # Packet Mirroring: send raw packets to server
 
# Capture settings remain unchanged
interface                = eth0
sipport                  = 5060
# No MySQL credentials needed on remote sensors for Local Processing mode
</syntaxhighlight>
 
Restart the service on each probe:
<syntaxhighlight lang="bash">
# On each probe
systemctl restart voipmonitor
</syntaxhighlight>
 
;5. Verify Connection in GUI:
# Log in to the VoIPmonitor GUI
# Navigate to '''Settings → Sensors'''
# Verify that probes appear automatically with their configured <code>id_sensor</code> values
# Check the connection status (online/offline)
 
;6. Test Data Flow:
# Generate test traffic on a probe network (make a test call)
# Check CDR view in GUI
# Verify that new records show the correct <code>id_sensor</code> for that probe
# Confirm PCAP files are accessible (click play button in CDR view)
 
==== Common Issues During Migration
 
{| class="wikitable" style="background:#e8f4f8; border:1px solid #4A90E2;"
|-
|-
! colspan="2" style="background:#4A90E2; color: white;" | Troubleshooting Connection Problems
| Sensor not connecting || <code>journalctl -u voipmonitor -f</code> on sensor || Check <code>server_destination</code>, password, firewall
|-
|-
| style="vertical-align: top;" | '''Probes cannot connect:'''
| Traffic rate <code>[0.0Mb/s]</code> || tcpdump on sensor interface || Network/SPAN issue, not communication
| * Verify <code>server_password</code> is identical on server and all probes
* Check firewall: allow incoming TCP on <code>server_bind_port</code> (default 60024) on central server
* Verify network connectivity: <code>nc -zv <server_ip> <server_bind_port></code> from probe
|-
|-
| style="vertical-align: top;" | '''All CDRs show same sensor:'''
| High memory on central server || Check if <code>sipport</code> includes 60024 || Exclude server port from sipport
| This typically indicates the old mirror mode configuration is still active or the <code>id_sensor</code> is not set on probes. Double-check that:
* Mirror parameters are commented out on both sides
* Each probe has a unique <code>id_sensor</code> value
* Services were restarted after configuration changes
|-
|-
| style="vertical-align: top;" | '''PCAP files not accessible:'''
| Missing calls || Compare <code>sipport</code> on probe vs central || Must match on both sides
| In Local Processing mode (<code>packetbuffer_sender=no</code>), PCAPs are stored on probes and retrieved via TCP port 5029. Ensure:
* Central server can reach each probe on TCP/5029
* Firewall allows TCP/5029 from central server to probes
|}
 
== Critical Requirement: SIP and RTP must be captured by the same sniffer instance ==
 
'''VoIPmonitor cannot reconstruct a complete call record if SIP signaling and RTP media are captured by different sniffer instances.'''
 
{| class="wikitable" style="background:#fff3cd; border:1px solid #ffc107;"
|-
|-
! colspan="2" style="background:#ffc107;" | Important: Single sniffer requirement
| "Bad password" error || GUI → Settings → Sensors || Delete stale sensor record, restart sensor
|-
|-
| style="vertical-align: top;" | '''What does not work:'''
| "Connection refused (111)" after migration || Check <code>server_destination</code> in config || Points to old server IP
| * Sniffer A in Availability Zone 1 captures SIP signaling
* Sniffer B in Availability Zone 2 captures RTP media
* Result: Incomplete call record, GUI cannot reconstruct the call
|-
|-
| style="vertical-align: top;" | '''Why:'''
| RTP streams end prematurely || Check <code>natalias</code> location || Configure only on central server
| Call correlation requires a '''single sniffer instance to process both SIP and RTP packets from the same call'''. The sniffer correlates SIP signaling (INVITE, BYE, etc.) with RTP media in real-time during packet processing. If packets are split across multiple sniffers, the correlation cannot occur.
|-
|-
| style="vertical-align: top;" | '''Solution:'''
| Time sync errors || <code>timedatectl status</code> || Fix NTP or increase tolerance
| Forward traffic so that '''one sniffer processes both SIP and RTP for each call'''. Options:
* Route both SIP and RTP through the same Availability Zone for capture
* Use Packet Mirroring mode to forward complete traffic (SIP+RTP) to a central server that processes everything
* Configure network routers/firewalls to forward the required stream to the correct zone
|}
|}


Configuration parameters like <code>receiver_check_id_sensor</code> and <code>cdr_check_exists_callid</code> are for other scenarios (multipath routing, duplicate Call-ID handling) and '''do NOT enable split SIP/RTP correlation'''. Setting these parameters does not allow SIP from one sniffer to be merged with RTP from another sniffer.
== Connection Testing ==


== Intermediate Server: Multi-Sensor Aggregation ==
<syntaxhighlight lang="bash">
# Test connectivity from sensor to server
nc -zv <server_ip> 60024


An intermediate server can receive traffic from multiple remote sensors and forward it to a central server. This is useful for aggregating traffic from many locations before sending to a central data center.
# Verify server is listening
ss -tulpn | grep voipmonitor


=== Architecture ===
# Check sensor logs
 
journalctl -u voipmonitor -n 100 | grep -i "connect"
<kroki lang="plantuml">
</syntaxhighlight>
@startuml
skinparam shadowing false
skinparam defaultFontName Arial
skinparam rectangle {
  BorderColor #4A90E2
  BackgroundColor #FFFFFF
}


rectangle "Remote Sensor A" as RA
== Time Synchronization Errors ==
rectangle "Remote Sensor B" as RB
rectangle "Remote Sensor C" as RC
rectangle "Intermediate Server\n(server_bind + server_destination)" as INT
rectangle "Central Server\n(server_bind)" as CS
database "MySQL" as DB


RA --> INT : encrypted TCP
If seeing "different time between server and client" errors:
RB --> INT : encrypted TCP
RC --> INT : encrypted TCP
 
INT --> CS : encrypted TCP
CS --> DB : CDRs
 
note right of INT
  Behavior controlled by
  packetbuffer_sender on
  intermediate server:
 
  * packetbuffer_sender=no:
    Process traffic locally,
    send CDRs to central
 
  * packetbuffer_sender=yes:
    Forward raw packets to
    central server
end note
@enduml
</kroki>
 
This is supported because the intermediate server does NOT do local packet capture - it only acts as a relay.
 
=== Intermediate Server Configuration ===
 
The intermediate server has both <code>server_bind</code> (to receive from remote sensors) and <code>server_destination</code> (to send to central server).


'''Immediate workaround:''' Increase tolerance on both sides:
<syntaxhighlight lang="ini">
<syntaxhighlight lang="ini">
# On INTERMEDIATE SERVER
client_server_connect_maximum_time_diff_s = 30
# Acts as server for remote sensors, client to central server
receive_packetbuffer_maximum_time_diff_s = 30
</syntaxhighlight>


[general]
'''Root cause fix:''' Ensure NTP is working:
id_sensor              = 100    # Unique ID for this intermediate server
<syntaxhighlight lang="bash">
timedatectl status          # Check sync status
chronyc tracking            # Check offset (Chrony)
ntpq -p                      # Check offset (NTP)
</syntaxhighlight>


# Receive from remote sensors (server role)
== Network Throughput Testing ==
server_bind            = 0.0.0.0
server_bind_port        = 60024
server_password        = sensor_password


# Send to central server (client role)
If experiencing "packetbuffer: MEMORY IS FULL" errors, test network with iperf3:
server_destination      = central.server.ip
server_destination_port = 60024
server_password        = central_password


# CRITICAL: packetbuffer_sender controls what happens to forwarded traffic
<syntaxhighlight lang="bash">
 
# On central server
# Option 1: Local Processing on intermediate server
iperf3 -s
packetbuffer_sender    = no      # Process locally, send CDRs to central
mysqlhost              = localhost
mysqldb                = voipmonitor
mysqluser              = voipmonitor
mysqlpassword          = db_password


# OR Option 2: Forward raw packets to central server
# On probe
# packetbuffer_sender  = yes    # Forward raw packets (no database needed here)
iperf3 -c <server_ip>
</syntaxhighlight>
</syntaxhighlight>
=== <code>packetbuffer_sender</code> on Intermediate Server ===
The <code>packetbuffer_sender</code> setting on the intermediate server determines how it handles traffic from remote sensors:


{| class="wikitable"
{| class="wikitable"
|-
|-
! Setting !! What Happens !! Storage Location
! Result !! Interpretation !! Action
|-
|-
| <code>packetbuffer_sender=no</code> || Intermediate server processes traffic (SIP/RTP analysis) and sends CDRs to central server || PCAPs on intermediate server
| Expected bandwidth (>900 Mbps on 1Gb) || Network OK || Check local CPU/RAM
|-
|-
| <code>packetbuffer_sender=yes</code> || Intermediate server forwards raw packets to central server, which processes them || PCAPs on central server
| Low throughput || Network bottleneck || Check switches, cabling, consider Local Processing mode
|}
|}


In both cases, the '''original remote sensors must still be manually added to the GUI for visibility'''
== Debugging SIP Traffic ==


=== Original vs Intermediate Sensor Visibility ===
<code>sngrep</code> does not work on the central server because traffic is encapsulated in the TCP tunnel.


{| class="wikitable" style="background:#e8f4f8; border:1px solid #4A90E2;"
'''Options:'''
|-
* '''Live Sniffer:''' Use GUI → Live Sniffer to view SIP from remote sensors
! colspan="2" style="background:#4A90E2; color: white;" | Important: Manual Sensor Registration
* '''sngrep on sensor:''' Run <code>sngrep -i eth0</code> directly on the remote sensor
|-
| style="vertical-align: top;" | '''Behavior:'''
| When using an intermediate server, the original remote sensors (A, B, C) are not automatically visible in the GUI Settings. Only the intermediate server itself appears.
|-
| style="vertical-align: top;" | '''Solution:'''
| To view statistics and status for the original sensors, they must be manually added to the GUI Settings list with their <code>id_sensor</code> values, even though they connect to the intermediate server rather than directly to the central server.
|}


=== Example: Local Processing Mode ===
== Stale Sensor Records ==


Remote sensors forward CDRs to intermediate server, which forwards them to central server:
If a new sensor fails with "bad password" despite correct credentials:


<syntaxhighlight lang="ini">
# Delete the sensor record from '''GUI → Settings → Sensors'''
# Remote Sensors (A, B, C)
# Restart voipmonitor on the sensor: <code>systemctl restart voipmonitor</code>
id_sensor              = 2        # Unique values: 2, 3, 4...
# The sensor will re-register automatically
server_destination      = intermediate.server.ip
server_destination_port = 60024
server_password        = sensor_password


packetbuffer_sender    = no      # Local Processing: process here, send CDRs
= Legacy: Mirror Mode =
interface              = eth0
sipport                = 5060
</syntaxhighlight>


<syntaxhighlight lang="ini">
The older <code>mirror_destination</code>/<code>mirror_bind</code> options still work but Client-Server mode is preferred (encryption, simpler management).
# Intermediate Server
server_bind            = 0.0.0.0
server_bind_port        = 60024
server_password        = sensor_password


server_destination     = central.server.ip
To migrate from mirror mode:
server_destination_port = 60024
# Stop sensors, comment out <code>mirror_*</code> parameters
server_password        = central_password
# Configure <code>server_bind</code> on central, <code>server_destination</code> on sensors
# Restart all services


packetbuffer_sender    = no      # Process locally, send CDRs onward
For mirror mode <code>id_sensor</code> attribution, use:
mysqlhost              = localhost
<syntaxhighlight lang="ini">
mysqldb                = voipmonitor
# On central receiver
mysqluser              = voipmonitor
mirror_bind_sensor_id_by_sender = yes
mysqlpassword          = db_password
</syntaxhighlight>
</syntaxhighlight>


<syntaxhighlight lang="ini">
= See Also =
# Central Server
server_bind            = 0.0.0.0
server_bind_port        = 60024
server_password        = central_password


mysqlhost              = localhost
* [[Sniffing_modes|Deployment & Topology Guide]] - Traffic forwarding methods
mysqldb                = voipmonitor
* [[Sniffer_configuration|Sniffer Configuration]] - All parameters reference
mysqluser              = voipmonitor
* [[Merging_or_correlating_multiple_call_legs|Call Correlation]] - Multi-leg call handling
mysqlpassword          = db_password
* [[FAQ#One_GUI_for_multiple_sniffers|FAQ: One GUI for Multiple Sniffers]]
</syntaxhighlight>


=== Example: Packet Mirroring Mode ===
== Filtering Options in Packet Mirroring Mode ==


Remote sensors forward raw packets to intermediate server, which forwards them to central server:
{{Note|1='''Important distinction:''' In Packet Mirroring mode (<code>packetbuffer_sender=yes</code>):


<syntaxhighlight lang="ini">
* '''Capture rules (GUI-based):''' Applied ONLY on the central server
# Remote Sensors (A, B, C)
* '''BPF filters / IP filters:''' CAN be applied on the remote sensor to reduce bandwidth
id_sensor              = 2        # Unique values: 2, 3, 4...
server_destination      = intermediate.server.ip
server_destination_port = 60024
server_password        = sensor_password


packetbuffer_sender    = yes    # Packet Mirroring: send raw packets
Use the following options on the '''remote sensor''' to filter traffic BEFORE sending to the central server:
interface              = eth0
sipport                = 5060
</syntaxhighlight>


<syntaxhighlight lang="ini">
<syntaxhighlight lang="ini">
# Intermediate Server
# On REMOTE SENSOR (client)
server_bind            = 0.0.0.0
server_bind_port        = 60024
server_password        = sensor_password


server_destination      = central.server.ip
# Option 1: BPF filter (tcpdump syntax) - most flexible
server_destination_port = 60024
filter = not net 192.168.0.0/16 and not net 10.0.0.0/8
server_password        = central_password


packetbuffer_sender    = yes    # Forward raw packets onward
# Option 2: IP allow-list filter - CPU-efficient, no negation support
# No database configuration needed on intermediate server
interface_ip_filter = 192.168.1.0/24
interface_ip_filter = 10.0.0.0/8
</syntaxhighlight>
</syntaxhighlight>


<syntaxhighlight lang="ini">
<b>Benefits of filtering on remote sensor:</b>
# Central Server
* Reduces WAN bandwidth usage between sensor and central server
server_bind            = 0.0.0.0
* Reduces processing load on central server
server_bind_port        = 60024
* Use <code>filter</code> for complex conditions (tcpdump/BPF syntax)
server_password        = central_password
* Use <code>interface_ip_filter</code> for simple IP allow-lists (more efficient)


mysqlhost              = localhost
<b>Filtering approaches:</b>
mysqldb                = voipmonitor
* For <b>SIP header-based filtering</b>: Apply capture rules on the '''central server''' only
mysqluser              = voipmonitor
* For <b>IP/subnet filtering</b>: Use <code>filter</code> or <code>interface_ip_filter</code> on '''remote sensor'''}}
mysqlpassword          = db_password


# Processing and storage options (configured on central server)
== Supported Configuration Options in Packet Mirroring Mode ==
sipport                = 5060
savertp                = yes
savesip                = yes
</syntaxhighlight>


== Version Compatibility ==
In Packet Mirroring mode (<code>packetbuffer_sender = yes</code>), the remote sensor forwards raw packets without processing them. This means many configuration options that manipulate packet behavior are '''unsupported''' on the remote sensor.


=== General Compatibility Rules ===
== Supported Options on Remote Sensor (packetbuffer_sender) ==


In general, there is **no strict version locking** between the VoIPmonitor GUI (web interface) and the Sniffer (sensor components). The primary compatibility constraint is the **Database Schema**, which is managed primarily by the GUI.
The following options work correctly on the remote sensor in packet mirroring mode:


{| class="wikitable"
{| class="wikitable"
! Parameter !! Description
|-
| <code>id_sensor</code> || Unique sensor identifier
|-
| <code>server_destination</code> || Central server address
|-
|-
! Scenario !! Compatibility !! Risk Level !! Details
| <code>server_destination_port</code> || Central server port (default 60024)
|-
|-
| '''GUI ≥ Sniffer''' || '''Compatible''' || ✅ Low || GUI is newer or same version. It can visualize data from older sensors, and the database schema supports all data the sensors write.
| <code>server_password</code> || Authentication password
|-
|-
| '''GUI < Sniffer''' || '''Potentially Incompatible''' || ⚠️ High || Sensor is newer. It may try to write to database columns or tables that do not exist in the older GUI's schema, leading to SQL insert errors.
| <code>server_destination_timeout</code> || Connection timeout settings
|}
|-
 
| <code>server_destination_reconnect</code> || Auto-reconnect behavior
**Best Practice:**
|-
> Maintain the GUI version equal to or higher than the sniffer version (GUI ≥ Sniffer).
| <code>filter</code> || BPF filter to limit capture (use this to capture only SIP)
 
|-
When upgrading components, always upgrade the GUI first so it applies new database schemas, then upgrade the sniffers.
| <code>interface_ip_filter</code> || IP-based packet filtering
 
|-
=== Client-Server Mode Version Matching ===
| <code>interface</code> || Capture interface
 
|-
For client-server mode deployments (remote sensors connecting to a central server), it is **strongly recommended that clients and receivers use the same version**.
| <code>sipport</code> || SIP ports to monitor
 
|-
{| class="wikitable" style="background:#fff3cd; border:1px solid #ffc107;"
| <code>promisc</code> || Promiscuous mode
|-
|-
! colspan="2" style="background:#ffc107;" | Version Matching Recommendation
| <code>rrd</code> || RRD statistics
|-
|-
| style="vertical-align: top;" | '''For client-server mode:'''
| <code>spooldir</code> || Temporary packet buffer directory
| Keep all sensors and their central receivers on the same version whenever possible. While different versions can work together, matching versions ensure full compatibility and access to the latest features and fixes.
|-
|-
| style="vertical-align: top;" | '''For gradual upgrades:'''
| <code>ringbuffer</code> || Ring buffer size for packet mirroring
| If you cannot upgrade all sensors simultaneously, upgrade the central receiver/server first, then upgrade sensors one by one. The receiver should be at least as new as the newest connecting sensor.
|}
 
=== Mixed Version Compatibility ===
 
If you need to run mixed versions in your deployment temporarily, a compatibility option is available in sensor version 2024.11.0 and newer.
 
<strong>server_cp_store_simple_connect_response</strong>
 
This configuration option enables the client-server communication protocol to work with mixed-version environments. When enabled, the server uses a simpler protocol variant that is compatible with older sensor versions.
 
<syntaxhighlight lang="ini">
# On the central receiver/server (sniffer 2024.11.0+)
server_cp_store_simple_connect_response = yes
</syntaxhighlight>
 
| Condition | Default Value | Recommended Setting |
|-----------|---------------|-------------------|
| Matching versions (normal) | no | no (default) |
| Mixed versions (temporary) | no | yes (enable only if needed) |
 
{| class="wikitable" style="background:#f8f9fa; border:1px solid #dee2e6;"
|-
|-
! colspan="2" style="background:#dee2e6;" | Important Notes on Mixed Versions
| <code>max_buffer_mem</code> || Maximum buffer memory
|-
|-
| This is a **temporary compatibility option** for migration periods. Using matching versions for all components is the preferred long-term configuration.
| <code>packetbuffer_enable</code> || Enable packet buffering
|-
|-
| The option should be set on the **central receiver/server** instance that receives connections from sensors.
| <code>packetbuffer_compress</code> || Enable compression for forwarded packets
|-
|-
| Once all sensors are upgraded to their target versions, disable this option (<code>server_cp_store_simple_connect_response = no</code>) for normal operation.
| <code>packetbuffer_compress_ratio</code> || Compression ratio
|}
|}


=== Version Verification ===
== Unsupported Options on Remote Sensor ==


To check the running version of any component:
The following options '''do NOT work''' on the remote sensor in packet mirroring mode because the sensor does not parse packets:


<syntaxhighlight lang="bash">
{| class="wikitable"
# On the sensor or server host
! Parameter !! Reason
/usr/local/sbin/voipmonitor --version
 
# Or via management API (default port 5029)
echo 'sniffer_version' | nc 127.0.0.1 5029
</syntaxhighlight
 
In the GUI, navigate to '''Settings → Sensors''' to see the version of each connected sensor.
 
== Limitations ==
 
* All sensors must use the same <code>server_password</code> at each connection level (sensors→intermediate and intermediate→central)
* '''A single sniffer cannot do local packet capture AND act as both server and client simultaneously.''' The intermediate server configuration works because it does NOT capture from its own network interface - it only receives from sensors and forwards to central server.
* Each sensor requires a unique <code>id_sensor</code> (< 65536)
* Time synchronization (NTP) is critical for correlating calls across sensors
* Maximum allowed time difference between client and server: 2 seconds (configurable via <code>client_server_connect_maximum_time_diff_s</code>)
 
For a complete reference of all client-server parameters, see [[Sniffer_configuration#Distributed_Operation:_Client/Server_&_Mirroring|Sniffer Configuration: Distributed Operation]].
 
=== Troubleshooting: Time Synchronization Errors ===
 
If sensors repeatedly log errors such as <code>send packetbuffer block error: failed response from server - different time between server and client</code> or <code>client_server_connect_maximum_time_diff</code>, this indicates that the clock offset between the client and server has exceeded the permitted limit.
 
{| class="wikitable" style="background:#fff3cd; border:1px solid #ffc107;"
|-
|-
! colspan="2" style="background:#ffc107;" | Time Synchronization Error
| <code>natalias</code> || NAT alias handling (configure on central server instead)
|-
|-
| style="vertical-align: top;" | '''Error Message:'''
| <code>rtp_check_both_sides_by_sdp</code> || RTP correlation requires packet parsing
| <code>send packetbuffer block error: failed response from server - different time between server and client</code>
|-
|-
| style="vertical-align: top;" | '''Meaning:'''
| <code>disable_process_sdp</code> || SDP processing happens on central server
| The actual time difference between client and server exceeds the configured threshold. Even if both systems are configured for UTC and use the same NTP servers, clock drift, NTP polling intervals, network latency to NTP servers, or firewall restrictions on UDP port 123 can cause the offset to exceed the limit.
|}
 
==== Solution 1: Increase Time Tolerance (Immediate Workaround) ====
 
If you cannot immediately resolve the NTP synchronization precision issue, increase the allowed time difference in the configuration.
 
Add or modify the following parameters in <code>/etc/voipmonitor.conf</code> on '''both the client and the server''':
 
<syntaxhighlight lang="ini">
# Increase time difference tolerance (in seconds)
# For persistent clock offset issues, consider values like 30 or higher
client_server_connect_maximum_time_diff_s = 30
receive_packetbuffer_maximum_time_diff_s = 30
</syntaxhighlight>
 
After changing the configuration, restart the VoIPmonitor service on both nodes:
 
<syntaxhighlight lang="bash">
systemctl restart voipmonitor
</syntaxhighlight>
 
{| class="wikitable" style="background:#e8f4f8; border:1px solid #4A90E2;"
|-
|-
! colspan="2" style="background:#4A90E2; color: white;" | Parameter Function
| <code>save_sdp_ipport</code> || SDP extraction happens on central server
|-
|-
| style="vertical-align: top;" | <code>client_server_connect_maximum_time_diff_s</code>
| <code>rtpfromsdp_onlysip</code> || RTP mapping requires packet parsing
| (Default: 2) Controls the maximum time difference allowed during the initial client-server connection handshake.
|-
|-
| style="vertical-align: top;" | <code>receive_packetbuffer_maximum_time_diff_s</code>
| <code>rtpip_find_endpoints</code> || Endpoint discovery requires packet parsing
| (Default: 30) Controls the maximum time difference allowed when clients send packet buffer data (CDRs or raw packets) to the server.
|}
|}


==== Solution 2: Verify and Fix NTP Synchronization (Root Cause Fix) ====
{{Warning|1='''Critical: Storage options''' (<code>savesip</code>, <code>savertp</code>, <code>saveaudio</code>) '''must be configured on the CENTRAL SERVER''' in packet mirroring mode. The remote sensor only forwards packets and does not perform any storage operations.}}


The proper solution is to ensure NTP is synchronized with minimal clock drift.
== SIP-Only Capture Example ==


'''Check NTP status on both Client and Server:'''
To capture and forward only SIP packets (excluding RTP/RTCP) for security or compliance:


<syntaxhighlight lang="bash">
<syntaxhighlight lang="ini">
# Check system time synchronization status
# /etc/voipmonitor.conf - Remote Sensor
timedatectl status
id_sensor              = 2
server_destination      = central.server.ip
server_destination_port = 60024
server_password        = your_strong_password
packetbuffer_sender    = yes
interface              = eth0
sipport                = 5060,5061


# Ensure "System clock synchronized: yes" is shown
# Filter to capture ONLY SIP packets (exclude RTP/RTCP)
filter = port 5060 or port 5061
</syntaxhighlight>
</syntaxhighlight>


'''Check clock offset (Chrony):'''
{{Note|1=The <code>filter</code> parameter using BPF syntax (tcpdump-compatible) is the recommended way to filter packets at the source in packet mirroring mode. This reduces bandwidth by forwarding only SIP packets to the central server.}}


<syntaxhighlight lang="bash">
chronyc tracking


# Look at "Last offset" and "RMS offset" values
# If values fluctuate near or above 2000ms (2 seconds), connections will fail
</syntaxhighlight>


'''Check clock offset (NTP):'''


<syntaxhighlight lang="bash">
ntpq -p


# Look at delay, offset, and jitter columns
# High jitter or offset will trigger sporadic errors
</syntaxhighlight>


Common NTP issues:
* Firewall silently dropping UDP port 123 (NTP)
* High network latency to NTP servers
* NTP service not running or misconfigured
* Different NTP server pools with divergent time


'''Verify firewall allows NTP:'''


<syntaxhighlight lang="bash">
= AI Summary for RAG =
# Check firewalld (CentOS/RHEL)
firewall-cmd --list-ports
 
# Check iptables/ufw (Debian/Ubuntu)
iptables -L -n -v | grep 123
# or
ufw status verbose | grep 123
</syntaxhighlight>
 
If needed, allow NTP traffic:


<syntaxhighlight lang="bash">
'''Summary:''' VoIPmonitor v20+ Client-Server architecture for distributed deployments using encrypted TCP (default port 60024, zstd compression). Two modes: '''Local Processing''' (<code>packetbuffer_sender=no</code>) analyzes locally and sends CDRs only (1Gb sufficient); '''Packet Mirroring''' (<code>packetbuffer_sender=yes</code>) forwards raw packets to central server. Critical requirements: (1) exclude server_bind_port from sipport on central server (prevents memory issues); (2) sipport must match on probe and central server; (3) single sniffer must process both SIP and RTP for same call; (4) natalias only on central server. Intermediate servers supported for hub-and-spoke topology. Use <code>manager_ip</code> to bind outgoing connections to specific IP on HA setups. Sensor health via management API port 5029: <code>echo 'sniffer_stat' | nc <ip> 5029</code>. Debug SIP using Live Sniffer in GUI or sngrep on remote sensor. Stale sensor records cause "bad password" errors - delete from GUI Settings → Sensors and restart. Time sync errors: fix NTP or increase <code>client_server_connect_maximum_time_diff_s</code>.
# firewalld
firewall-cmd --permanent --add-service=ntp
firewall-cmd --reload


# ufw
'''Keywords:''' distributed architecture, client-server, packetbuffer_sender, local processing, packet mirroring, server_destination, server_bind, sipport exclusion, AWS VPC Traffic Mirroring alternative, intermediate server, sensor health, sniffer_stat, Live Sniffer, natalias, version compatibility, time synchronization, NTP, stale sensor record, mirror mode migration, manager_ip, high availability
ufw allow ntp
</syntaxhighlight>


== AI Summary for RAG ==
'''Summary:''' VoIPmonitor v20+ uses Client-Server architecture for distributed deployments with encrypted TCP connections (default port 60024 with zstd compression, configurable via server_bind_port and server_destination_port). Two modes: Local Processing (<code>packetbuffer_sender=no</code>) analyzes locally and sends CDRs, Packet Mirroring (<code>packetbuffer_sender=yes</code>) forwards raw packets. NETWORK BANDWIDTH REQUIREMENTS: For Local Processing (PCAPs stored on sensors), network traffic consists mainly of CDR SQL data and a 1Gb connection between sensors and central server is generally sufficient. For Packet Mirroring, bandwidth consumption is roughly equivalent to VoIP traffic volume (use <code>server_type_compress=zstd</code> to reduce). Dashboard widgets for SIP/RTP/REGISTER counts: with Packet Mirroring, statistics appear only on central server (sender has empty widgets); with Local Processing, statistics appear on both sensor and central server. To enable local statistics on a forwarding sensor, set <code>packetbuffer_sender=no</code> (increases CPU/RAM usage). Supports failover with multiple server IPs. CDRs stored centrally; PCAPs on sensors (Local Processing) or centrally (Packet Mirroring). In Packet Mirroring mode, the <code>save*</code> options (savertp, savesip, saveaudio) configured on the CENTRAL SERVER control storage for packets received from sensors. When multiple sensors forward packets with the same Call-ID, VoIPmonitor automatically merges them into a single CDR. To keep records separate per sensor with same Call-ID, run multiple receiver instances on different ports with separate database tables. CRITICAL: A single sniffer instance MUST process both SIP signaling and RTP media for the same call. Splitting SIP and RTP across different sniffers creates incomplete call records that cannot be reconstructed. INTERMEDIATE SERVER: An intermediate server can receive traffic from multiple remote sensors and forward it to a central server. The intermediate server has both <code>server_bind</code> (to receive from sensors) and <code>server_destination</code> (to send to central server). The behavior is controlled by <code>packetbuffer_sender</code> on the intermediate server: if <code>packetbuffer_sender=no</code>, it processes traffic locally and sends CDRs to central server; if <code>packetbuffer_sender=yes</code>, it forwards raw packets to central server. In both cases, the original remote sensors must be manually added to the GUI Settings for visibility. This is supported because the intermediate server does NOT do local packet capture - it only acts as a relay. For custom port configuration: server_bind_port on central server MUST match server_destination_port on remote sensors. Common reasons for custom ports: firewall restrictions, multiple instances on same server, compliance requirements, avoiding port conflicts. SENSOR HEALTH CHECK VIA MANAGEMENT API: Each sensor exposes a TCP management API (default port 5029) that can be queried via netcat: `echo 'sniffer_stat' | nc <sensor_ip> <sensor_port>`. This returns JSON with sensor status including running state, version, uptime, active calls, total calls, packets per second, and packet drops. IMPORTANT: There is NO single command to check all sensors simultaneously - each must be queried individually. Scripting multiple sensors with a loop can provide a consolidated result with exit codes. In newer VoIPmonitor versions, management API communication may be encrypted, requiring encryption to be disabled or using VoIPmonitor-specific CLI tools. Firewall must allow TCP port 5029 access from monitoring host to sensors. DEBUGGING SIP TRAFFIC IN DISTRIBUTED ARCHITECTURE: Standard packet capture tools like sngrep cannot see SIP packets on the central server in Client-Server mode because traffic is encapsulated inside encrypted TCP tunnel (port 60024 for Packet Mirroring, or SQL/3306 for Local Processing). SOLUTION 1: Use Live Sniffer feature in VoIPmonitor GUI - navigate to Live Sniffer, select remote sensor from dropdown, click Start to view live SIP packets from that sensor. Live Sniffer streams SIP packets from sensor to GUI in real-time via Manager API (TCP 5029), with features including call coloring by Call-ID, packet details inspection, call flow visualization, and multi-user support. SOLUTION 2: Run sngrep directly on the remote sensor machine where traffic first arrives from network interface before encapsulation: sngrep -i eth0 (replace eth0 with actual interface connected to SPAN/mirror port). VERIFICATION: Check connectivity on central server with `tcpdump -i any port 60024` for Packet Mirroring mode, `tcpdump -i any port 3306` for Local Processing mode, or check sensor statistics: `echo 'sniffer_stat' | nc <sensor_ip> 5029`. For detailed Live Sniffer setup and troubleshooting, see Live_sniffer documentation. LEGACY MIRROR MODE: Older mirror_destination/mirror_bind options exist but are less robust (no encryption, UDP) and Client-Server mode is recommended. Symptoms of mirror mode issues: all CDRs incorrectly associated with a single sensor after system updates. Migration involves: stop probes, remove old sensor records from GUI Settings, comment out mirror parameters (mirror_bind_ip, mirror_bind_port, mirror_destination_ip, mirror_destination_port), add server_bind/server_bind_port on central server and server_destination/server_destination_port on probes, set unique id_sensor per probe, choose packetbuffer_sender mode. Common migration issues: probes cannot connect (verify server_password, firewall allows TCP on server_bind_port), all CDRs show same sensor (old mirror config still active or id_sensor not set), PCAPs not accessible in Local Processing mode (central server must reach probes on TCP/5029). TROUBLESHOOTING: In distributed/probe setups with Packet Mirroring, if a probe is not detecting all calls on expected ports, the <code>sipport</code> configuration MUST match on BOTH the probe AND the central analysis host. If the network uses multiple SIP ports (e.g., 5060, 5061, 5080), both systems must have all ports listed in their <code>sipport</code> directive. Common symptom: Probe sees traffic via <code>tcpdump</code> but central server records incomplete CDRs. RTP STREAMS END PREMATURELY: If RTP streams end prematurely in call recordings when using a remote sniffer with a central GUI, this is often caused by Incorrect <code>natalias</code> configuration placement. The <code>natalias</code> option must be configured ONLY on the central server that receives and processes packets, NOT on the remote sniffer that captures and forwards them. When packets are forwarded from a remote sniffer to a central server in Packet Mirroring mode, configuring <code>natalias</code> on the remote sniffer causes IP address substitution to happen at capture time, which causes the central server's RTP correlation logic to fail. Solution: Remove <code>natalias</code> from the remote sniffer's voipmonitor.conf, add it to the central server's voipmonitor.conf, then restart both services. WEB GUI ACCESSIBLE BUT SENSORS CANNOT CONNECT: If the web portal is accessible but sensors cannot connect to the primary server, verify that the MySQL/MariaDB database service on the central server is running and responsive. The central VoIPmonitor service requires a functioning database connection to accept sensor data, even though the web interface (PHP) may remain accessible. Check MySQL service status (<code>systemctl status mariadb</code> or <code>systemctl status mysqld</code>) and inspect MySQL error logs (<code>/var/log/mariadb/mariadb.log</code> or <code>/var/log/mysql/error.log</code>) for critical errors. Restart the database service if needed. VERSION COMPATIBILITY: There is no strict version locking between GUI and sensor components. The primary compatibility constraint is the database schema managed by the GUI. Best practice: Maintain GUI version equal to or higher than sensor version (GUI >= Sniffer). When upgrading, upgrade the GUI first to apply new database schemas, then upgrade sensors. For client-server mode, it is strongly recommended that clients and receivers use the same version for full compatibility and access to latest features. If mixed versions are needed temporarily, sensor version 2024.11.0+ supports <code>server_cp_store_simple_connect_response = yes</code> configuration option on the central receiver/server to enable a simpler protocol compatible with older sensor versions. This is a temporary compatibility option for migration periods - disable (<code>server_cp_store_simple_connect_response = no</code>) once all components are on matching versions. Check versions with <code>/usr/local/sbin/voipmonitor --version</code> or via management API: <code>echo 'sniffer_version' | nc 127.0.0.1 5029</code>. In the GUI, navigate to Settings -> Sensors to see sensor versions.
TIME SYNCHRONIZATION ERRORS: In client-server mode, sensors may log errors like "send packetbuffer block error: failed response from server - different time between server and client" or "client_server_connect_maximum_time_diff" when clock offset exceeds the permitted limit. Even if both systems use UTC and same NTP servers, clock drift, NTP polling intervals, network latency to NTP servers, or firewall restrictions on UDP port 123 can cause the offset to exceed the threshold. IMMEDIATE WORKAROUND: Increase time tolerance by adding `client_server_connect_maximum_time_diff_s = 30` and `receive_packetbuffer_maximum_time_diff_s = 30` to voipmonitor.conf on BOTH client and server, then restart voipmonitor service. The `client_server_connect_maximum_time_diff_s` parameter (default: 2) controls maximum time difference during initial client-server connection handshake. The `receive_packetbuffer_maximum_time_diff_s` parameter (default: 30) controls maximum time difference when clients send packet buffer data (CDRs or raw packets) to the server. ROOT CAUSE FIX: Ensure NTP is synchronized with minimal clock drift. Check system time status with `timedatectl status` (ensure "System clock synchronized: yes"), check clock offset with `chronyc tracking` (look at Last offset and RMS offset - values near or above 2000ms cause failures), or use `ntpq -p` (look at delay, offset, jitter columns). Common NTP issues: firewall silently dropping UDP port 123, high network latency to NTP servers, NTP service not running or misconfigured, different NTP server pools with divergent time. Allow NTP traffic through firewall: `firewall-cmd --permanent --add-service=ntp` (firewalld) or `ufw allow ntp` (Ubuntu/Debian).
'''Keywords:''' distributed architecture, client-server, network bandwidth, throughput, network requirements, 1Gb connection, bandwidth requirements, server_destination, server_bind, server_bind_port, server_destination_port, custom port, packetbuffer_sender, local processing, packet mirroring, remote sensors, failover, encrypted channel, zstd compression, dashboard widgets, statistics, empty dashboard, SIP RTP correlation, split sensors, single sniffer requirement, availability zone, savertp, savesip, saveaudio, centralized storage, packet storage control, call-id merging, multiple sensors same callid, separate records per sensor, receiver instances, mysqltableprefix, firewall, port configuration, connection troubleshooting, probe, central host, central server, sensor, sipport, missing calls, probe not detecting calls, tcpdump, configuration mismatch, mirror mode, migration, mirror_destination, mirror_bind, mirror_bind_ip, mirror_bind_port, mirror_destination_ip, mirror_destination_port, migrate from mirror mode, all CDRs same sensor, system update, upgrade, intermediate server, relay server, multi-sensor aggregation, hub and spoke, chained topology, sensor forwarding, mysql, mariadb, database service, web gui accessible, error logs, sensor health check, management API, sniffer_stat, TCP port 5029, manager_bind, nc netcat, sensor status, sensor monitoring, health status, exit code, consolidated result, check all sensors, encrypted API, encryption disabled, natalias, NAT alias configuration, RTP streams end prematurely, RTP correlation, IP address substitution, NAT traversal, remote sniffer configuration, central server configuration, natalias placement, incomplete recordings, call recordings cut off, version compatibility, GUI version, sensor version, database schema, GUI >= Sniffer, upgrade GUI first, client-server version matching, mixed versions, server_cp_store_simple_connect_response, protocol compatibility, sniffer 2024.11.0, check version, sniffer_version, time synchronization, NTP, clock drift, time difference, different time, send packetbuffer block error, failed response from server, client_server_connect_maximum_time_diff_s, receive_packetbuffer_maximum_time_diff_s, timedatectl, chronyc tracking, ntpq -p, clock offset, UDP port 123, firewall NTP, DEBUGGING SIP, sngrep, live sniffer, cannot see SIP packets, encrypted TCP tunnel, packet encapsulation, sngrep central server, debug SIP distributed architecture, live sniffer remote sensor, packet capture tools, manager API live sniffer, call coloring, packet details, call flow visualization, encrypted tunnel traffic, zstd compression, packetbuffer_sender traffic, SQL traffic local processing
'''Key Questions:'''
'''Key Questions:'''
* How do I connect multiple VoIPmonitor sensors to a central server?
* How do I connect multiple VoIPmonitor sensors to a central server?
* What is the expected network throughput between remote sensors and the central GUI/Database server?
* What is the difference between Local Processing and Packet Mirroring mode?
* Is a 1Gb network connection sufficient for remote sensors in VoIPmonitor distributed deployment?
* Why is VoIPmonitor using high memory on the central server?
* What network bandwidth is required for Local Processing mode vs Packet Mirroring mode?
* Why is a remote probe not detecting all calls on expected ports?
* What is the difference between Local Processing and Packet Mirroring?
* How do I check VoIPmonitor sensor health status?
* Where are CDRs and PCAP files stored in distributed mode?
* Why does a new sensor fail with "bad password" error?
* What is packetbuffer_sender and when should I use it?
* How do I configure failover for remote sensors?
* Why are dashboard widgets (SIP/RTP/REGISTER counts) empty for a sensor configured to forward packets?
* How do I enable local statistics on a forwarding sensor?
* Can a VoIPmonitor instance act as an intermediate server receiving from multiple sensors and forwarding to a central server?
* How does packetbuffer_sender control traffic forwarding on an intermediate server?
* Can a VoIPmonitor sniffer be both a server (listening for sensors) and a client (sending to central server)?
* Why does a single sniffer cannot be both server and client mean, and what are the exceptions?
* How do I configure an intermediate server in a hub-and-spoke topology?
* Do I need to manually add remote sensors to the GUI when using an intermediate server?
* How does an intermediate server handle traffic from multiple remote sensors in Packet Mirroring mode?
* How does an intermediate server handle traffic from multiple remote sensors in Local Processing mode?
* Can VoIPmonitor reconstruct a call if SIP signaling is captured by one sniffer and RTP media by another?
* Why does receiver_check_id_sensor not allow merging SIP from one sensor with RTP from another?
* How do I control packet storage when sensors send raw packets to a central server?
* What happens when multiple sensors see the same Call-ID?
* How do I keep records separate when multiple sensors see the same Call-ID?
* How do I configure a custom port for client-server connections?
* What do I do if probes cannot connect to the VoIPmonitor server?
* Why is my remote sensor showing connection refused or timeout?
* Why is a voipmonitor sensor probe not detecting all calls on expected ports?
* Do I need to configure sipport on both the probe and central server in distributed setups?
* What happens if sipport configuration doesn't match between probe and central host?
* How do I migrate from mirror mode to client-server mode?
* How do I migrate from mirror mode to client-server mode?
* Why are all CDRs incorrectly associated with a single sensor after a system update?
* What causes time synchronization errors between client and server?
* What are the differences between mirror mode and client-server mode?
* Where should natalias be configured in distributed deployments?
* How do I configure mirror_destination and server_destination?
* Can VoIPmonitor act as an intermediate server?
* Why are sensors unable to connect to the VoIPMonitor primary server while the web portal remains accessible?
* What is an alternative to AWS VPC Traffic Mirroring?
* What should I check if the web GUI works but sensors cannot connect to the central server?
* How do I verify MySQL or MariaDB database service is running on the primary server?
* Where are MySQL error logs located?
* How do I check the health status of a VoIPmonitor sensor?
* What is the command to query sensor status via the management API?
* How do I use sniffer_stat to check sensor health?
* Is there a single command to check all sensors at once?
* How do I check the status of multiple sensors and get a consolidated exit code?
* What is the default management API port for VoIPmonitor sensors?
* Why can I not connect to the sensor management API on TCP port 5029?
* How do I check if sensor management API is encrypted?
* How do I check the health of remote sensors in a distributed deployment?
* Why are RTP streams ending prematurely in call recordings when using a remote sniffer with central GUI?
* Why is sngrep not showing SIP packets on the central server in distributed mode?
* Can I see SIP packets with sngrep when using Client-Server architecture?
* How do I debug SIP traffic in VoIPmonitor distributed architecture?
* How do I inspect SIP packets from remote sensors?
* What is Live Sniffer and how do I use it for remote sensors?
* How do I view live SIP packets from remote sensors?
* Can I run sngrep on the central server with distributed architecture?
* Where should I run sngrep in a VoIPmonitor distributed setup?
* How do I use Live Sniffer to debug remote sensors?
* How do I verify the encrypted tunnel is working between sensor and central server?
* Where should I configure natalias in a distributed VoIPmonitor deployment?
* Do I need to configure natalias on the remote sensor or on the central server?
* What happens if natalias is configured on both the remote sensor and central server?
* What is the version compatibility between the VoIPmonitor GUI and sniffer components?
* Can I use a newer GUI with an older sniffer?
* What happens if I use an older GUI with a newer sniffer?
* Do I need to match the GUI version with the sniffer version?
* Do remote sensors and central receivers need the same version in client-server mode?
* Is it safe to run different versions of VoIPmonitor sensors and receivers?
* How do I handle mixed versions in a client-server deployment?
* What is server_cp_store_simple_connect_response used for?
* When should I enable server_cp_store_simple_connect_response?
* How do I use server_cp_store_simple_connect_response for mixed version compatibility?
* How do I check the running version of my VoIPmonitor sensor or GUI?* What does the error "send packetbuffer block error: failed response from server - different time between server and client" mean?
* How do I fix time synchronization errors between VoIPmonitor client and server?
* What are client_server_connect_maximum_time_diff_s and receive_packetbuffer_maximum_time_diff_s?
* How do I increase the time tolerance for VoIPmonitor distributed sensors?
* How do I check if NTP is synchronized on VoIPmonitor sensors?
* How do I check clock offset between VoIPmonitor client and server?
* How do I fix different time errors in VoIPmonitor client-server mode?

Latest revision as of 20:48, 19 January 2026


This guide covers deploying multiple VoIPmonitor sensors in a distributed architecture using Client-Server mode (v20+).

For deployment options including on-host vs dedicated sensors and traffic forwarding methods (SPAN, GRE, TZSP, VXLAN), see VoIPmonitor Deployment & Topology Guide.

Overview

VoIPmonitor v20+ uses Client-Server architecture for distributed deployments. Remote sensors connect to a central server via encrypted TCP (default port 60024, zstd compression).

Mode packetbuffer_sender What is Sent Processing Location Use Case
Local Processing no (default) CDRs only Remote sensor Multi-site, low bandwidth
Packet Mirroring yes Raw packets Central server Centralized analysis, low-resource remotes

Use Cases

AWS VPC Traffic Mirroring Alternative: If experiencing packet loss with AWS VPC Traffic Mirroring (VXLAN overhead, MTU fragmentation), use client-server mode instead:

  • Install VoIPmonitor on each source EC2 instance
  • Send via encrypted TCP to central server
  • Eliminates VXLAN encapsulation and MTU issues

Configuration

Remote Sensor (Client)

id_sensor               = 2                    # Unique per sensor (1-65535)
server_destination      = central.server.ip
server_destination_port = 60024
server_password         = your_strong_password

# Choose mode:
packetbuffer_sender     = no     # Local Processing: analyze locally, send CDRs
# packetbuffer_sender   = yes    # Packet Mirroring: send raw packets

interface               = eth0
sipport                 = 5060
# No MySQL credentials needed on remote sensors

💡 Tip: For HA setups with floating IPs, use manager_ip = 10.0.0.5 to bind outgoing connections to a static IP address.

Central Server

server_bind             = 0.0.0.0
server_bind_port        = 60024
server_password         = your_strong_password

mysqlhost               = localhost
mysqldb                 = voipmonitor
mysqluser               = voipmonitor
mysqlpassword           = db_password

# If receiving raw packets (packetbuffer_sender=yes on clients):
sipport                 = 5060
savertp                 = yes
savesip                 = yes

⚠️ Warning: Critical: Exclude server_bind_port from sipport on the central server. Including it causes continuously increasing memory usage. 

# WRONG - includes sensor communication port:
sipport = 1-65535

# CORRECT - excludes port 60024:
sipport = 1-60023,60025-65535

Key Configuration Rules

Rule Applies To Why
server_bind_port must match server_destination_port Both Connection fails if mismatched
sipport must match on probe and central server Packet Mirroring Missing ports = missing calls
natalias only on central server Packet Mirroring Prevents RTP correlation issues
Each sensor needs unique id_sensor All Required for identification

Local Processing vs Packet Mirroring

Local Processing Packet Mirroring
packetbuffer_sender no (default) yes
Processing location Remote sensor Central server
PCAP storage Remote sensor Central server
WAN bandwidth Low (CDRs only, 1Gb sufficient) High (full packets)
Remote CPU load Higher Minimal
Capture rules applied On sensor On central server only

PCAP Access in Local Processing Mode

PCAPs are stored on remote sensors. The GUI retrieves them through the central server, which proxies the request to the sensor over the existing TCP/60024 connection - the same persistent encrypted channel the sensor uses for sending CDRs. This connection is bidirectional; the central server does not open any separate connection back to the sensor.

Firewall requirements:

Direction Port Purpose
Remote sensors → Central server TCP/60024 Persistent encrypted channel (CDRs from sensor, PCAP requests from server - bidirectional)
GUI → Central server TCP/5029 Manager API (sensor status, active calls, configuration)
GUI → Central server TCP/60024 Server API (list connected sensors, proxy PCAP retrieval)

ℹ️ Note: The central server does not initiate connections to remote sensors. All server↔sensor communication happens over the single TCP/60024 connection that the sensor established.

💡 Tip: Packet Mirroring (packetbuffer_sender=yes) automatically deduplicates calls - the central server merges packets from all probes for the same Call-ID into a single unified CDR. This also ensures one logical call only consumes one license channel.

Advanced Topics

High Availability (Failover)

Remote sensors can specify multiple central servers: 

server_destination = 192.168.0.1, 192.168.0.2

If primary is unavailable, the sensor automatically connects to the next server.

Connection Compression

# On both client and server (default: zstd)
server_type_compress = zstd   # Options: zstd, gzip, lzo, none

Intermediate Server (Hub-and-Spoke)

An intermediate server can receive from multiple sensors and forward to a central server: 

# On INTERMEDIATE SERVER
id_sensor               = 100

# Receive from remote sensors
server_bind             = 0.0.0.0
server_bind_port        = 60024
server_password         = sensor_password

# Forward to central server
server_destination      = central.server.ip
server_destination_port = 60024

packetbuffer_sender     = no    # or yes, depending on desired mode

ℹ️ Note: This works because the intermediate server does NOT do local packet capture - it only relays. Original remote sensors must be manually added to GUI Settings for visibility.

Multiple Receivers for Packet Mirroring

⚠️ Warning: Multiple sensors with packetbuffer_sender=yes sending to a single receiver instance can cause call processing conflicts (calls appear in Active Calls but missing from CDRs).

Solution: Run separate receiver instances on different hosts, each dedicated to specific sensors: 

# Receiver Instance 1 (Host 1, for Sensor A)
server_bind_port        = 60024
id_sensor               = 1

# Receiver Instance 2 (Host 2, for Sensor B)
server_bind_port        = 60024
id_sensor               = 2

Alternative: Use Local Processing mode (packetbuffer_sender=no) which processes calls independently on each sensor.

Preventing Duplicate CDRs (Local Processing)

When multiple probes capture the same call in Local Processing mode: 

# On each probe
cdr_check_exists_callid = yes

This checks for existing CDRs before inserting. Requires MySQL UPDATE privileges.

Critical: SIP and RTP Must Be Captured Together

VoIPmonitor cannot correlate SIP and RTP from different sniffer instances. A single sniffer must process both SIP and RTP for each call. Parameters like cdr_check_exists_callid do NOT enable split SIP/RTP correlation.


Split SIP/RTP with Packet Mirroring Mode

ℹ️ Note: Exception for Packet Mirroring Mode:: The above limitation applies to Local Processing mode (packetbuffer_sender=no) where each sensor processes calls independently. In Packet Mirroring mode (packetbuffer_sender=yes), the central server receives raw packets from multiple remote sensors and processes them together. This allows scenarios where SIP and RTP are captured on separate nodes - configure both as packet senders and let the central server correlate them into single unified CDRs.

Example scenario: Separate SIP signaling node and RTP handling node: 

# SIP Signaling Node (packet sender)
id_sensor               = 1
packetbuffer_sender     = yes
server_destination      = central.server.ip
server_destination_port = 60024
server_password         = your_password

# RTP Handling Node (packet sender)
id_sensor               = 2
packetbuffer_sender     = yes
server_destination      = central.server.ip
server_destination_port = 60024
server_password         = your_password

The central server merges packets from both senders by Call-ID, creating unified CDRs with complete SIP and RTP data.


HEP Protocol in Client/Server Mode

VoIPmonitor supports receiving HEP-encapsulated traffic on sniffer clients and forwarding it to a central server. This enables distributed capture from HEP sources (Kamailio, OpenSIPS, rtpproxy, FreeSWITCH) in a client/server architecture.

Scenario: SIP proxy and RTP proxy at different locations sending HEP to remote sniffer clients: 

# Remote Sniffer Client A (receives HEP from Kamailio)
id_sensor               = 1
hep                     = yes
hep_bind_port           = 9060
packetbuffer_sender     = yes
server_destination      = central.server.ip
server_destination_port = 60024
server_password         = your_password

# Remote Sniffer Client B (receives HEP from rtpproxy)
id_sensor               = 2
hep                     = yes
hep_bind_port           = 9060
packetbuffer_sender     = yes
server_destination      = central.server.ip
server_destination_port = 60024
server_password         = your_password

The central server receives packets from both clients and correlates them into unified CDRs using standard SIP Call-ID and IP:port from SDP.

ℹ️ Note: This also works for IPFIX (Oracle SBCs) and RibbonSBC protocols forwarded via client/server mode.

Alternative: Direct HEP to single sniffer

If both HEP sources can reach the same sniffer directly, no client/server setup is needed: 

# Single sniffer receiving HEP from multiple sources
hep                     = yes
hep_bind_port           = 9060
interface               = eth0   # Can also sniff locally if needed

Both Kamailio (SIP) and rtpproxy (RTP) send HEP to this sniffer on port 9060. The sniffer correlates them automatically based on Call-ID and SDP IP:port.

Sensor Health Monitoring

Management API

Query sensor status via TCP port 5029: 

echo 'sniffer_stat' | nc <sensor_ip> 5029

Returns JSON with status, version, active calls, packets per second, etc.

Multi-Sensor Health Check Script

#!/bin/bash
SENSORS=("192.168.1.10:5029" "192.168.1.11:5029")
for SENSOR in "${SENSORS[@]}"; do
    IP=$(echo $SENSOR | cut -d: -f1)
    PORT=$(echo $SENSOR | cut -d: -f2)
    STATUS=$(echo 'sniffer_stat' | nc -w 2 $IP $PORT 2>/dev/null | grep -o '"status":"[^"]*"' | cut -d'"' -f4)
    echo "$IP: ${STATUS:-FAILED}"
done

Version Compatibility

Scenario Compatibility Notes
GUI ≥ Sniffer ✅ Compatible Recommended
GUI < Sniffer ⚠️ Risk Sensor may write to non-existent columns

Best practice: Upgrade GUI first (applies schema changes), then upgrade sensors.

For mixed versions temporarily, add to central server: 

server_cp_store_simple_connect_response = yes   # Sniffer 2024.11.0+

Troubleshooting

Quick Diagnosis

Symptom First Check Likely Cause
Sensor not connecting journalctl -u voipmonitor -f on sensor Check server_destination, password, firewall
Traffic rate [0.0Mb/s] tcpdump on sensor interface Network/SPAN issue, not communication
High memory on central server Check if sipport includes 60024 Exclude server port from sipport
Missing calls Compare sipport on probe vs central Must match on both sides
"Bad password" error GUI → Settings → Sensors Delete stale sensor record, restart sensor
"Connection refused (111)" after migration Check server_destination in config Points to old server IP
RTP streams end prematurely Check natalias location Configure only on central server
Time sync errors timedatectl status Fix NTP or increase tolerance

Connection Testing

# Test connectivity from sensor to server
nc -zv <server_ip> 60024

# Verify server is listening
ss -tulpn | grep voipmonitor

# Check sensor logs
journalctl -u voipmonitor -n 100 | grep -i "connect"

Time Synchronization Errors

If seeing "different time between server and client" errors:

Immediate workaround: Increase tolerance on both sides: 

client_server_connect_maximum_time_diff_s = 30
receive_packetbuffer_maximum_time_diff_s = 30

Root cause fix: Ensure NTP is working: 

timedatectl status           # Check sync status
chronyc tracking             # Check offset (Chrony)
ntpq -p                      # Check offset (NTP)

Network Throughput Testing

If experiencing "packetbuffer: MEMORY IS FULL" errors, test network with iperf3: 

# On central server
iperf3 -s

# On probe
iperf3 -c <server_ip>
Result Interpretation Action
Expected bandwidth (>900 Mbps on 1Gb) Network OK Check local CPU/RAM
Low throughput Network bottleneck Check switches, cabling, consider Local Processing mode

Debugging SIP Traffic

sngrep does not work on the central server because traffic is encapsulated in the TCP tunnel.

Options:

  • Live Sniffer: Use GUI → Live Sniffer to view SIP from remote sensors
  • sngrep on sensor: Run sngrep -i eth0 directly on the remote sensor

Stale Sensor Records

If a new sensor fails with "bad password" despite correct credentials:

  1. Delete the sensor record from GUI → Settings → Sensors
  2. Restart voipmonitor on the sensor: systemctl restart voipmonitor
  3. The sensor will re-register automatically

Legacy: Mirror Mode

The older mirror_destination/mirror_bind options still work but Client-Server mode is preferred (encryption, simpler management).

To migrate from mirror mode:

  1. Stop sensors, comment out mirror_* parameters
  2. Configure server_bind on central, server_destination on sensors
  3. Restart all services

For mirror mode id_sensor attribution, use: 

# On central receiver
mirror_bind_sensor_id_by_sender = yes

See Also

Filtering Options in Packet Mirroring Mode

ℹ️ Note: Important distinction: In Packet Mirroring mode (packetbuffer_sender=yes):

  • Capture rules (GUI-based): Applied ONLY on the central server
  • BPF filters / IP filters: CAN be applied on the remote sensor to reduce bandwidth

Use the following options on the remote sensor to filter traffic BEFORE sending to the central server: 

# On REMOTE SENSOR (client)

# Option 1: BPF filter (tcpdump syntax) - most flexible
filter = not net 192.168.0.0/16 and not net 10.0.0.0/8

# Option 2: IP allow-list filter - CPU-efficient, no negation support
interface_ip_filter = 192.168.1.0/24
interface_ip_filter = 10.0.0.0/8

Benefits of filtering on remote sensor:

  • Reduces WAN bandwidth usage between sensor and central server
  • Reduces processing load on central server
  • Use filter for complex conditions (tcpdump/BPF syntax)
  • Use interface_ip_filter for simple IP allow-lists (more efficient)

Filtering approaches:

  • For SIP header-based filtering: Apply capture rules on the central server only
  • For IP/subnet filtering: Use filter or interface_ip_filter on remote sensor

Supported Configuration Options in Packet Mirroring Mode

In Packet Mirroring mode (packetbuffer_sender = yes), the remote sensor forwards raw packets without processing them. This means many configuration options that manipulate packet behavior are unsupported on the remote sensor.

Supported Options on Remote Sensor (packetbuffer_sender)

The following options work correctly on the remote sensor in packet mirroring mode:

Parameter Description
id_sensor Unique sensor identifier
server_destination Central server address
server_destination_port Central server port (default 60024)
server_password Authentication password
server_destination_timeout Connection timeout settings
server_destination_reconnect Auto-reconnect behavior
filter BPF filter to limit capture (use this to capture only SIP)
interface_ip_filter IP-based packet filtering
interface Capture interface
sipport SIP ports to monitor
promisc Promiscuous mode
rrd RRD statistics
spooldir Temporary packet buffer directory
ringbuffer Ring buffer size for packet mirroring
max_buffer_mem Maximum buffer memory
packetbuffer_enable Enable packet buffering
packetbuffer_compress Enable compression for forwarded packets
packetbuffer_compress_ratio Compression ratio

Unsupported Options on Remote Sensor

The following options do NOT work on the remote sensor in packet mirroring mode because the sensor does not parse packets:

Parameter Reason
natalias NAT alias handling (configure on central server instead)
rtp_check_both_sides_by_sdp RTP correlation requires packet parsing
disable_process_sdp SDP processing happens on central server
save_sdp_ipport SDP extraction happens on central server
rtpfromsdp_onlysip RTP mapping requires packet parsing
rtpip_find_endpoints Endpoint discovery requires packet parsing

⚠️ Warning: Critical: Storage options (savesip, savertp, saveaudio) must be configured on the CENTRAL SERVER in packet mirroring mode. The remote sensor only forwards packets and does not perform any storage operations.

SIP-Only Capture Example

To capture and forward only SIP packets (excluding RTP/RTCP) for security or compliance: 

# /etc/voipmonitor.conf - Remote Sensor
id_sensor               = 2
server_destination      = central.server.ip
server_destination_port = 60024
server_password         = your_strong_password
packetbuffer_sender     = yes
interface               = eth0
sipport                 = 5060,5061

# Filter to capture ONLY SIP packets (exclude RTP/RTCP)
filter = port 5060 or port 5061

ℹ️ Note: The filter parameter using BPF syntax (tcpdump-compatible) is the recommended way to filter packets at the source in packet mirroring mode. This reduces bandwidth by forwarding only SIP packets to the central server.





AI Summary for RAG

Summary: VoIPmonitor v20+ Client-Server architecture for distributed deployments using encrypted TCP (default port 60024, zstd compression). Two modes: Local Processing (packetbuffer_sender=no) analyzes locally and sends CDRs only (1Gb sufficient); Packet Mirroring (packetbuffer_sender=yes) forwards raw packets to central server. Critical requirements: (1) exclude server_bind_port from sipport on central server (prevents memory issues); (2) sipport must match on probe and central server; (3) single sniffer must process both SIP and RTP for same call; (4) natalias only on central server. Intermediate servers supported for hub-and-spoke topology. Use manager_ip to bind outgoing connections to specific IP on HA setups. Sensor health via management API port 5029: echo 'sniffer_stat' | nc <ip> 5029. Debug SIP using Live Sniffer in GUI or sngrep on remote sensor. Stale sensor records cause "bad password" errors - delete from GUI Settings → Sensors and restart. Time sync errors: fix NTP or increase client_server_connect_maximum_time_diff_s.

Keywords: distributed architecture, client-server, packetbuffer_sender, local processing, packet mirroring, server_destination, server_bind, sipport exclusion, AWS VPC Traffic Mirroring alternative, intermediate server, sensor health, sniffer_stat, Live Sniffer, natalias, version compatibility, time synchronization, NTP, stale sensor record, mirror mode migration, manager_ip, high availability

Key Questions:

  • How do I connect multiple VoIPmonitor sensors to a central server?
  • What is the difference between Local Processing and Packet Mirroring mode?
  • Why is VoIPmonitor using high memory on the central server?
  • Why is a remote probe not detecting all calls on expected ports?
  • How do I check VoIPmonitor sensor health status?
  • Why does a new sensor fail with "bad password" error?
  • How do I migrate from mirror mode to client-server mode?
  • What causes time synchronization errors between client and server?
  • Where should natalias be configured in distributed deployments?
  • Can VoIPmonitor act as an intermediate server?
  • What is an alternative to AWS VPC Traffic Mirroring?
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