Cisco Cisco Agent Desktop 8.5 Guia De Configuração Rápida
Introduction
November 2013
45
To illustrate this,
shows an IP phone connected to a router, then connected
to a switch. A VoIP server is connected to the same switch and SPAN is configured to
capture traffic on the port to which the router is connected. When on a call with
another phone, the phone sends out a packet of audio data addressed to the other IP
phone at 192.168.252.33.
capture traffic on the port to which the router is connected. When on a call with
another phone, the phone sends out a packet of audio data addressed to the other IP
phone at 192.168.252.33.
The VoIP server knows that the MAC address of the agent phone is 0024AF774BC1,
so it sets its packet filter to grab only those audio packets where the source or
destination MAC address in the Ethernet header match 0024AF774BC1. The RTP
packet sent from the phone has the correct source MAC address, but the destination
MAC is not that of the other phone—it is the router’s MAC address, which is the next
hop of the packet to be routed to the other IP phone. When the router routes the
packet, it is now the sender of the packet and the source MAC address is set to that of
the router. Routers are layer-2 devices, so they will change MAC addresses, but not IP
addresses, which are layer-3 entities.
so it sets its packet filter to grab only those audio packets where the source or
destination MAC address in the Ethernet header match 0024AF774BC1. The RTP
packet sent from the phone has the correct source MAC address, but the destination
MAC is not that of the other phone—it is the router’s MAC address, which is the next
hop of the packet to be routed to the other IP phone. When the router routes the
packet, it is now the sender of the packet and the source MAC address is set to that of
the router. Routers are layer-2 devices, so they will change MAC addresses, but not IP
addresses, which are layer-3 entities.
Figure 23.
MAC address alteration by network routing