This is on a 6509/Sup720 IOS 12.2(18)SXF5 and 12.2(18)SXE, and a WS-X6548-GE-TX and a WS-X6724-SFP blade.

I'm trying to create two sub-interfaces on each port, tag one for a data vlan and one for a voice vlan. Each port will then connect to a 3750 switch where IP phones and PC's will be connected to the same port. This is the typical IP phone/PC architecture. I was hoping to use the same vlan numbers on each switch so we don't have to keep track of which vlan is which switch - this works in the layer 2 world because the vlan stops at the layer 3 router port.

Well on the 6509 port this is what I have for the first port:

interface GigabitEthernet2/14

description to SW-232.15

no ip address

no ip route-cache

speed 1000

duplex full

mls qos trust dscp

spanning-tree portfast

!

interface GigabitEthernet2/14.10

encapsulation dot1Q 10

ip address 162.*.*.1 255.255.255.128 (the data vlan)

no ip route-cache

!

interface GigabitEthernet2/14.910 (the voice vlan)

encapsulation dot1Q 910

ip address 172.*.*.1 255.255.255.128

no ip route-cache

Now when I go to the next interface and do the same thing this is the error msg I get:

ENGLAB-6513-Native(config-if)#int g2/16.10

ENGLAB-6513-Native(config-subif)#encapsulation dot1Q 10

Command rejected: VLAN 10 not available

I can put some other dot1q tag on here but not 10 which I've already used.

Aren't these dot1q tags used only between the interface and the layer 2 switch connected to it? Aren't the tags stripped off when packets switch from one interface to another?

If so shouldn't I be able to use the same dot1q tag on different sub-interfaces?

Or am I not understanding things correctly?