Networking

Cisco: VLAN(s) not available in Port Manager

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

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