Cisco – Understand the behavior for hub/switch in Cisco IP phone 7960

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Cisco IP phone 7960 has two RJ45 sockets at back panel. One of those ports has "10/100 SW" label above and other port has "10/100 PC" label. According to "Network Port 2 Device Type" under phone "Network Setup" menu it is a "Hub/Switch". If I view the MAC address table from switch where the phone is connected to, then I see following information:

Destination Address  Address Type  VLAN  Destination Port
-------------------  ------------  ----  --------------------
000a.b42f.54bb       Dynamic        105  FastEthernet0/2
0030.94c3.1597       Dynamic        105  FastEthernet0/2
0030.94c3.1597       Dynamic        909  FastEthernet0/2

000a.b42f.54bb is the MAC address of my PC and 0030.94c3.1597 is the MAC address of the phone.

Am I correct that Cisco IP phone 7960 has a two port switch? Why is there a MAC address table entry for 0030.94c3.1597 in VLAN 105 when according to phone the operational VLAN ID is 909?

Best Answer

It really is a 3 port switch:

  • One port connects to the PC
  • One port connects to the upstream switch
  • One port connects internally to the phone

The reason you see the MAC address on V105 is that the internal switch sends CDP, LLDP, STP, etc on the native VLAN, using that MAC address.

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