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New Member

Trunking on CSS

It looks like you can't trunk and bridge the same vlan on the CSS. As soon as you include a vlan on a trunk, the CSS wants to tag the packets going out bridged ports belonging to the same vlan. Any way round this?

Thanks

  • Application Networking
6 REPLIES
Cisco Employee

Re: Trunking on CSS

euuhhh...sorry but that's not the case in my lab.

I have tons of config with trunk and regular interface both using the same vlan.

What CSS ?

What version ?

Are you sure about what you saw ?

How did you check ?

Thanks,

Gilles.

New Member

Re: Trunking on CSS

Hi Gilles,

CSS is 11506 ver 07.50.1.03

The config looks like this:

bridge spanning-tree disabled

interface 1/1

trunk

vlan 51

default-vlan

interface 1/2

bridge vlan 51

Port 1/1 connects to a 6509 on port 3/5 which is a trunk with only vl 51 enabled. Port 1/2 connects to 3/6 which is in vl 801. When I enable the bridge port I get "Rcved 1Q-BPDU on non-trunk port 3/6 vlan 801 from 00-d0-c0-d6-ca-28" and the port goes into type-pvid-inc. I don't know if this is because it has seen a tagged packet or because it doesn't like the trunk stp mac address. I disabled stp on vl51 on the 6509, but no change.

regards

Simon

Cisco Employee

Re: Trunking on CSS

Simon,

the default-vlan means native vlan on the CSS.

So the CSS expects untagged frame for vlan 51 on interface 1/1.

Because the frame received is tagged, I assume the CSS does not know what to do with it and it bridges it out interface 1/2.

I would suggest to remove the command 'default-vlan' or configure the same native vlan on your Cat6k.

Regards,

Gilles.

Thanks for rating this answer.

New Member

Re: Trunking on CSS

Gilles,

I tried native and non native and changed the vlan setting on the cat so they matched, but no change. The problem is the cat changes its mac address for stp when you enable a trunk and the css doesn't recognise this. The css then bridges the packets out the other interfaces which the cat doesn't like. I think it's more likely the packet is not tagged and that it's the mac address arriving on a non-trunk port which is upsetting the cat.

I had a look on the css, but I couldn't see any way to filter a particular destination mac address.

regards

Simon

Cisco Employee

Re: Trunking on CSS

Simon,

do you have spanning-tree enabled or disabled on the CSS ?

Thanks,

Gilles.

New Member

Re: Trunking on CSS

Gilles,

I tried enabled and disabled. Also tried disabling on the cat for the vlan on the trunk, but the cat still sends the stp frames with the modified mac address as stp is enabled upstream on a different switch. I don't want to turn off stp across the network.

regards

Simon

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