MPLS and IRB on distinct sub-interfaces

Unanswered Question
Sep 4th, 2009

Hello,

We are actually running an MPLS network, and we need for a specific project to bridge one VLAN between a couple of routers and switches.

But, if we try to bridge the vlan on the routers using dot1q sub-interfaces on an interface which is also running an mpls sub-interface, it seems it is just not compatible:

example config:

interface GigabitEthernet1/0.505

encapsulation dot1Q 505

ip address 1.1.1.1 255.255.255.252

mpls ip

!

interface GigabitEthernet1/0.2598

encapsulation dot1Q 2598

Tryout 1:

Router#conf t

Router(config)#int Gi1/0.2598

Router(config-subif)#bridge-group 1

Interface has MPLS configuration

GigabitEthernet1/0.2598 cannot be configured into a Bridge Group

The reverse is also true:

Router(config)#int Gi1/0.505

Router(config-subif)#no mpls ip

Router(config-subif)#exit

Router(config)#int Gi1/0.2598

Router(config-subif)#bridge-group 1

Router(config)#int Gi1/0.505

Router(config-subif)#mpls ip

% MPLS not supported on interface GigabitEthernet1/0.505

Transparent bridging already configured

I naively thought that the configurations being applied on different sub-interfaces, in different dot1q domains, it would be somewhat segmented, and there would be no problems...

I'm more used to switches than routers, and I'd be curious to know the reasons for such a limitation on the 7200 platform (or in ios routers in general?).

Thanks,

Regards.

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Laurent Aubert Fri, 09/04/2009 - 05:32

Hi,

Both feature are incompatible due to the way both feature are implemented in IOS.

If you want to transport a VLAN across your MPLS backbone, you should consider EoMPLS.

HTH

hdecreis Fri, 09/04/2009 - 12:42

Hi,

Thanks for your answer,

> Both feature are incompatible due to the way both feature are implemented in IOS.

Yes, I sort of guessed that ;-) I was just curious about the soft/hard architectural reason behind it, I'll parse some technotes...

> If you want to transport a VLAN across your MPLS backbone, you should consider EoMPLS.

Sure, but the goal wasn't to transport the vlan accross the mpls backbone [sorry, I now realize that wasn't very clear in my post], just to add some redundancy at the edge of it [squared 2 7200 (in bb, running mpls) x 2 3560 (edge, no mpls)] using basic l2, "keeping it simple" [the two 7200 are directly connected].

Putting Eompls for this just add complexity, I guess I'll fallback to L3 redundancy. Sigh. When I first read about IRB, I was so happy that I had finally found the Catalyst SVI counterpart on routers platforms.

Thanks for your help,

Regards.

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