Sniffing modes

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This guide covers VoIPmonitor deployment options: where to install the sensor, how to forward traffic, and distributed architectures for multi-site monitoring.

Sensor Deployment Options

On-Host Capture

Install the sensor directly on the same Linux server as your PBX/SBC.

Pros Cons
No extra hardware, network changes, or port mirroring required Adds CPU, memory, and disk I/O load to production voice server
Simplest setup Not suitable if resources are critical

ℹ️ Note: VoIPmonitor sensor runs exclusively on Linux. For Windows-based PBXs (e.g., 3CX Windows edition), you must use a dedicated Linux sensor with traffic mirroring.

Dedicated Sensor

A separate Linux server runs only VoIPmonitor. Recommended for production environments as it isolates monitoring from voice platform resources.

When Required:

  • Windows-based PBXs
  • Limited CPU/RAM/disk I/O on PBX server
  • Zero monitoring impact needed
  • Centralized capture from multiple sites

Traffic Forwarding Methods

When using a dedicated sensor, you must forward traffic to it using one of these methods.

Hardware Port Mirroring (SPAN/RSPAN)

Physical or virtual switches copy traffic from source port(s) to a monitoring port.

Physical Switch

Configure your switch to mirror traffic from PBX/SBC ports to the sensor's port. Consult your switch documentation for specific commands. 

# /etc/voipmonitor.conf
interface = eth0
sipport = 5060
savertp = yes

💡 Tip:

VMware/ESXi Virtual Switch

For virtualized environments, VMware provides port mirroring at the virtual switch level.

Standard vSwitch:

  1. In vSphere Client, navigate to ESXi host
  2. Select virtual switch → Properties/Edit Settings → Enable Port Mirroring
  3. Set source (SBC VM) and destination (VoIPmonitor VM) ports

Distributed vSwitch:

  1. In vSphere Web Client → Networking → Select distributed switch
  2. Configure tab → Port Mirroring → Create mirroring session
  3. Specify source/destination ports and enable

ℹ️ Note: Distributed switch mirroring can span multiple ESXi hosts within a cluster.

Multiple VoIP Platforms

Monitor multiple platforms (e.g., Mitel + FreeSWITCH) with a single sensor by mirroring multiple source ports to one destination port.

GUI differentiation:

  • Filter by IP address ranges
  • Filter by number prefixes
  • Use separate sensors with unique id_sensor values

⚠️ Warning: Critical: When sniffing from multiple mirrored sources, packets may arrive as duplicates. Add auto_enable_use_blocks = yes to voipmonitor.conf to enable automatic deduplication. See Sniffer_configuration for details.

Software-based Tunneling

When hardware mirroring is unavailable, use software tunneling to encapsulate and forward packets.

Protocol Configuration Parameter Notes
IP-in-IP, GRE, ERSPAN Built-in (auto-detected) No additional config needed
TZSP (MikroTik) udp_port_tzsp = 37008
L2TP udp_port_l2tp = 1701
VXLAN udp_port_vxlan = 4789 Common in cloud environments
AudioCodes udp_port_audiocodes = 925 See AudioCodes Tunneling
IPFIX (Oracle SBCs) ipfix* options Enable ipfix options in config

HEP (Homer Encapsulation Protocol)

Lightweight protocol for mirroring VoIP packets. Supported by Kamailio, OpenSIPS, FreeSWITCH, and many SBCs. 

# /etc/voipmonitor.conf
hep = yes
hep_bind_port = 9060
hep_bind_udp = yes
# Optional: hep_kamailio_protocol_id_fix = yes

Known Limitations:

⚠️ Warning: HEP Correlation ID Not Supported: VoIPmonitor does NOT use HEP correlation ID (captureNodeID) to correlate SIP and RTP packets. If SIP and RTP arrive from different HEP sources, they will NOT be correlated into a single CDR.

VoIPmonitor correlates using standard SIP Call-ID, To/From tags, and RTP SSRC fields only. Feature request VS-1703 has been logged but there is no workaround currently.

HEP Timestamp: VoIPmonitor uses the HEP timestamp field. If the source has an unsynchronized clock, call timestamps will be incorrect. There is no option to ignore HEP timestamps.

HEP3 with Port 0: Not captured by default. Add port 0 to sipport: 

sipport = 0,5060

Cloud Packet Mirroring

Cloud providers offer native mirroring services using VXLAN or GRE encapsulation.

Provider Service Name
Google Cloud Packet Mirroring
AWS Traffic Mirroring
Azure Virtual Network TAP

Configuration Steps:

  1. Create a VoIPmonitor sensor VM in your cloud environment
  2. Create mirroring policy: select source VMs/subnets, set destination to sensor VM
  3. Critical: Capture traffic in BOTH directions (INGRESS and EGRESS)
  4. Configure sensor:
udp_port_vxlan = 4789
interface = eth0
sipport = 5060

⚠️ Warning: Capturing only ingress or only egress results in incomplete CDRs and broken call data.

Best Practices:

  • Filter at source to forward only SIP/RTP ports
  • Monitor NIC bandwidth limits
  • Account for VXLAN overhead (~50 bytes) - may need jumbo frames
  • Ensure NTP sync across all VMs

Alternative: Consider Client/Server architecture with on-host sensors instead of cloud mirroring for better performance.

Pre-Deployment Verification

For complex setups (RSPAN, ERSPAN, proprietary SBCs), verify compatibility before production deployment:

  1. Configure test mirroring with a subset of traffic
  2. Capture test calls with tcpdump: sudo tcpdump -i eth0 -s0 port 5060 -w /tmp/test.pcap
  3. Verify pcap contains SIP and RTP: tshark -r /tmp/test.pcap -Y "sip || rtp"
  4. Submit pcap to VoIPmonitor support with hardware/configuration details

Distributed Architectures

For multi-site monitoring, sensors can be deployed in various configurations.

Classic Mode: Standalone Sensors

Each sensor operates independently:

  • Processes packets and stores PCAPs locally
  • Connects directly to central MySQL to write CDRs
  • GUI needs network access to each sensor's TCP/5029 for PCAP retrieval

Alternative: NFS/SSHFS Mounting

If TCP/5029 access is blocked, mount remote spool directories on the GUI server: 

# NFS mount
sudo mount -t nfs 10.224.0.101:/var/spool/voipmonitor /mnt/voipmonitor/sensor1

# SSHFS mount
sshfs voipmonitor@10.224.0.101:/var/spool/voipmonitor /mnt/voipmonitor/sensor1

Configure GUI: Settings > System Configuration > Sniffer data path: /var/spool/voipmonitor:/mnt/voipmonitor/sensor1:/mnt/voipmonitor/sensor2

💡 Tip: For NFS, use hard,nofail,tcp mount options for reliability.

Modern Mode: Client/Server (v20+) — Recommended

Secure encrypted TCP channel between remote sensors and central server. GUI communicates only with central server.

Mode Processing PCAP Storage WAN Traffic Best For
Local Processing (packetbuffer_sender=no) Remote Remote Low (CDRs only) Limited WAN bandwidth
Packet Mirroring (packetbuffer_sender=yes) Central Central High (full packets) Low-resource remote sites

For detailed configuration, see Distributed Architecture: Client-Server Mode.

Quick Start - Remote Sensor (Local Processing): 

id_sensor               = 2
server_destination      = 10.224.0.250
server_destination_port = 60024
server_password         = your_strong_password
packetbuffer_sender     = no
interface               = eth0
sipport                 = 5060
# No MySQL credentials needed - central server writes to DB

Quick Start - Central Server: 

server_bind             = 0.0.0.0
server_bind_port        = 60024
server_password         = your_strong_password
mysqlhost               = 10.224.0.201
mysqldb                 = voipmonitor
mysqluser               = voipmonitor
mysqlpassword           = db_password
cdr_partition           = yes
interface               =   # Leave empty - don't sniff locally

Firewall Requirements

Deployment Port Direction Purpose
Client/Server TCP/60024 Remote → Central Encrypted CDR/packet channel
Client/Server TCP/5029 Central → Remote On-demand PCAP fetch (Local Processing mode)
GUI Access TCP/5029 GUI → Central Management/API
Cloud Mode TCP/60023 Sensor → cloud.voipmonitor.org Cloud service connection

Configuration Notes

Critical Parameters

Parameter Description Notes
id_sensor Unique sensor identifier (1-65535) Mandatory in distributed deployments
cdr_partition Enable daily CDR table partitions Enable on server writing to DB
mysqlloadconfig Load config from database Enable on central server only
interface Capture interface Use specific NIC or any

Time Synchronization

⚠️ Warning: Accurate NTP sync is critical for correlating call legs across sensors. All servers (GUI, DB, sensors) must run NTP client (chrony or ntpd).

First Startup

On first start against empty database:

  1. Start service: systemctl start voipmonitor
  2. Monitor logs: journalctl -u voipmonitor -f
  3. Wait for schema/partition creation to complete

If you see Table 'cdr_next_1' doesn't exist errors, check DB connectivity and privileges.

Deployment Comparison

Model Processing PCAP Storage WAN Traffic GUI Connectivity
Classic Standalone Remote Remote Minimal (MySQL CDRs) GUI ↔ each Sensor
Client/Server (Local Processing) Remote Remote Minimal (encrypted CDRs) GUI ↔ Central only
Client/Server (Packet Mirroring) Central Central High (encrypted packets) GUI ↔ Central only

Troubleshooting

NFS/SSHFS Connectivity

Missing data for specific time periods usually indicates storage server connectivity issues.

Symptom Likely Cause Solution
Data gap in time period NFS/SSHFS server unreachable Check logs for "not responding, timed out"
Stale file handle Server rebooted or export changed Remount NFS share
Connection resets Network interruption Check network stability
GUI shows "File not found" Mount point dismounted grep nfs 
# Check for NFS errors
grep "nfs: server.*not responding" /var/log/syslog
grep "nfs.*timed out" /var/log/syslog

# Verify mount status
mount | grep nfs
stat /mnt/voipmonitor/sensor1

See Also

AI Summary for RAG

Summary: VoIPmonitor deployment guide covering sensor placement (on-host vs dedicated), traffic forwarding methods (SPAN/RSPAN, software tunneling, cloud mirroring), and distributed architectures. Key traffic forwarding options: hardware port mirroring (physical/VMware switches), software tunnels (GRE, ERSPAN, TZSP, VXLAN, HEP, AudioCodes, IPFIX), and cloud provider services (GCP Packet Mirroring, AWS Traffic Mirroring, Azure Virtual Network TAP). CRITICAL HEP LIMITATION: VoIPmonitor does NOT use HEP correlation ID (captureNodeID) - SIP and RTP from different HEP sources will NOT be correlated (feature request VS-1703, no workaround). HEP3 packets with port 0 require adding port 0 to sipport directive. Cloud mirroring requires BIDIRECTIONAL capture (ingress+egress) or CDRs will be incomplete. Distributed architectures: Classic standalone (each sensor writes to central DB, GUI connects to each sensor) vs Modern Client/Server (recommended, encrypted TCP/60024 channel, GUI connects only to central server). Client/Server modes: Local Processing (packetbuffer_sender=no, CDRs only, PCAPs remain remote) vs Packet Mirroring (packetbuffer_sender=yes, full packets sent to central). Alternative for blocked TCP/5029: mount remote spools via NFS/SSHFS, configure multiple paths in GUI Sniffer data path setting. NFS troubleshooting: check for "not responding, timed out" in logs, verify mount status, use hard,nofail,tcp mount options. Critical requirement: NTP sync across all servers.

Keywords: deployment, topology, on-host, dedicated sensor, SPAN, RSPAN, port mirroring, VMware, vSwitch, dvSwitch, tunneling, GRE, ERSPAN, TZSP, VXLAN, HEP, HEP correlation ID, captureNodeID, VS-1703, HEP port 0, sipport, AudioCodes, IPFIX, cloud mirroring, GCP, AWS, Azure, Packet Mirroring, Traffic Mirroring, ingress, egress, bidirectional, client server, packetbuffer_sender, local processing, packet mirroring, TCP 60024, TCP 5029, NFS, SSHFS, sniffer data path, NTP, time synchronization, id_sensor, cdr_partition

Key Questions:

  • Should I install VoIPmonitor on my PBX or use a dedicated sensor?
  • How do I configure port mirroring (SPAN) for VoIPmonitor?
  • How do I configure VMware/ESXi virtual switch mirroring?
  • What software tunneling protocols does VoIPmonitor support?
  • How do I configure HEP (Homer Encapsulation Protocol)?
  • Does VoIPmonitor use HEP correlation ID to correlate SIP and RTP?
  • Why are SIP and RTP from different HEP sources not correlated?
  • How do I capture HEP3 packets with port 0?
  • How do I configure cloud packet mirroring (GCP/AWS/Azure)?
  • Why do I get incomplete CDRs with cloud mirroring?
  • What is the difference between classic and client/server deployment?
  • What is the difference between local processing and packet mirroring mode?
  • How do I access PCAPs if TCP/5029 is blocked?
  • How do I configure NFS/SSHFS for remote spool access?
  • How do I troubleshoot missing data with NFS mounts?
  • What firewall ports are required for client/server mode?
  • Why is NTP important for distributed VoIPmonitor?
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