Most of you will know that on cisco switches VLAN id’s 1002 – 1005 are reserved for backwards compatibility.
1002 fddi-default act/unsup 1003 token-ring-default act/unsup 1004 fddinet-default act/unsup 1005 trnet-default act/unsup
What I noticed today is that on some cisco systems (like f.e. Catalyst 4500) use a VLAN for traffic to a routed port. These VLAN’s start from 1006.
You can check which VLAN’s are in use for routed switchports by using the command “show vlan internal usage”.
switch#show running-config interface GigabitEthernet0/1 ! interface GigabitEthernet0/1 description Routed no switchport ip address 192.168.0.1 255.255.255.0 end switch#show vlan internal usage VLAN Usage ---- -------------------- 1006 GigabitEthernet0/1
When you really need to use a VLAN id used by a routed port you can do this by disabling the routed port, creating the vlan and then enabling the routed port again. Be aware that the switch will use the next VLAN in line.
switch(config)#int Gi0/1 switch(config-if)#shut switch(config)#do show vlan internal usage VLAN Usage ---- -------------------- switch(config)#vlan 1006 switch(config-vlan)#exit switch(config)#int Gi0/1 switch(config-if)#no shut switch(config-if)#exit switch(config)#do show vlan internal usa VLAN Usage ---- -------------------- 1007 FastEthernet0/24