Switchport operational mode on a port with an IP Phone connected

October 26, 2008 at 1:36 am | Posted in QoS, Switching | Leave a comment

What is the default switchport mode when you connect an IP Phone to a Cisco switch? It should be trunk, isn’t it. Otherwise, how it can carry two VLAN, one for Voice, and one for Data.

The “show interface switchport” output seems to show the contrary.

SW2 (fa0/1) -------- IP Phone --------- BB1 (simulating a PC)

Rack1SW2#sh cdp nei | in Phone
                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone
SEP0002B9BBCCF9     Fas 0/1               160            H P      IP Phone 7Port 1
BB1#sh cdp nei | in Phone
SEP0002B9BBCCF9     Eth 0              173          H        IP Phone  Port 2

Rack1SW2#sh arp         
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet                0   00e0.1e67.f6fe  ARPA   Vlan10
Internet                -   0014.a86b.df46  ARPA   Vlan10
Internet                -   0014.a86b.df47  ARPA   Vlan20
Internet                0   0002.b9ac.1af9  ARPA   Vlan20

Rack1SW2#sh run int fa0/1
Building configuration...

Current configuration : 86 bytes
interface FastEthernet0/1
 switchport access vlan 10
 switchport voice vlan 20

Interface              IP-Address      OK? Method Status                Protocol
Vlan8               YES NVRAM  up                    up     
Vlan10               YES manual up                    up     
Vlan20               YES manual up                    up   


Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/4/9 ms

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/8 ms

Rack1SW2#sh int fa0/1 switchport
Name: Fa0/1
Switchport: Enabled
Administrative Mode: dynamic auto
Operational Mode: static access
Administrative Trunking Encapsulation: negotiate
Operational Trunking Encapsulation: native
Negotiation of Trunking: On
Access Mode VLAN: 10 (VLAN0010)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
Voice VLAN: 20 (VLAN0020)
Administrative private-vlan host-association: none
Administrative private-vlan mapping: none
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk private VLANs: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL

Protected: false
Unknown unicast blocked: disabled
Unknown multicast blocked: disabled
Appliance trust: none

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