dot1Q native VLAN not working

[Kevin Dorrell]

I have a problem on a 2611 router running 12.2(15)T17. I do not seem to be able to run a native VLAN other than 1. I am trying to set up my native VLAN as VLAN 11. It works fine with the native on VLAN 1 (i.e. VLAN 11 is tagged), but not with VLAN 11 untagged:

<b>

interface Ethernet0/0.11

encapsulation dot1Q 11 native

ip address 172.16.26.3 255.255.255.0

</b>

On my switch, I have switchport trunk native vlan 11, and on the switch I see the router's MAC address on VLAN 11. But I cannot ping from the router to any other device on VLAN 11. If I do a debug arp on the router, this is what I get:

Mar 1 00:01:34.835: IP ARP: sent req src 172.16.26.3 0050.735e.4540, dst 172.16.26.2 0000.0000.0000 Ethernet0/0.11

Mar 1 00:01:34.835: IP ARP rep filtered src 172.16.26.2 00d0.c0f6.8760, dst 172.16.26.3 0050.735e.4540 wrong cable, interface Ethernet0/0.

It looks like the router is generating the ARP OK on VLAN 11, but fails to bind the response to the VLAN 11 sub-interface.

I know the router is not tagging the ARP going out, because if I change the native VLAN on the switch to some other value, then the switch sees the router MAC address on that value. So the transmission is definitely not tagged, but the reception is failing to bind to the VLAN 11 interface.

The switch is a 2950 running 12.1(22)EA5a.

Has anyone else ever seen this behaviour?

Kevin Dorrell

Luxembourg

[tdrais · Accepted solution]

Not sure if they ever fixed this. The 2600 support of 802.1q on ethernet has always done this.

I have never seen a official fix for this but if you configure a IP on the physical address that interface will act as the native VLAN. It does not seem to ever work to put the native keyword on a sub interface.

I am kinda surprised that you can run ip on both the physical and the sub interfaces but it does work.

[Kevin Dorrell]

Thanks. It's re-assuring to know that it is a known bug, and not something I am doing wrong. That is where experience comes into the picture!

The really strange thing is how it only applies to Ethernet interfaces and not FastEthernet. My 2620, running the same software version, can take a native VLAN quite happily.

Do you happen to know a bug number? I tried looking for it in the bug database but I didn't find anything.

Kevin Dorrell

Luxembourg

[tdrais]

I don't think it has a fix. Even the very latest version of the code does this. I have looked many times for the fix for this. Now that the routers are EoL I suspect it will never be fixed.