Quick Setup Guide

Configuring and Troubleshooting VoIP Monitoring
44 November 2013
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A Layer 2 routing device is any networking hardware that changes the MAC address of
a packet as it traverses the network. Routers, gateways, bridges, and hubs are all
examples of Layer 2 routing devices. Just about anything other than a network
repeater will cause the MAC address of packets flowing through it to change.
It is unusual to see a hardware configuration where a router is found inline between
the agent desktop and the agent's phone as shown on the left in Figure 22. It is more
likely to be seen when the packet capture software is running on the VoIP Monitor
server. Some networks are very complex and it might not be easy to tell if an IP phone
is connected directly to the switch or not.
If this configuration is used, MAC address filtering will fail, resulting in no audio for
monitored or recorded calls. The reason is that packets being sent over a network will
always use the source MAC address of the network device sending the packet and the
destination MAC of the next network device along the way toward the packet's
destination. The source and destination IP address and port will not change, though,
unless it hits a device using NAT or PAT (Figure 23).
Figure 22. Invalid hardware configuration