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Community Member

MPLS and VLANs

I have a situation whereby any subnet that is advertised by MPLS becomes immediately unreachable. One of the routers that is meant to forward the data has VLAN enabled on the MPLS interface the traffic is then untagged by our provider before it is forwarded to the other router as untagged traffic. I was wondering whether this could be the cause of the lack of communication.

5 REPLIES
Community Member

Re: MPLS and VLANs

The network looks as follows:

R1 --- R2 --- provider --- R3 --- R4

The interface on R2 has VLAN on its interface while the corresponding interface on R3 doesn't. Any subnet advertised on MPLS from R1 or R4 becomes unreachable despite the fact that the labels are propagating as expected. But R2 and R3 MPLS subnets are communicating.

Silver

Re: MPLS and VLANs

Sorry, but the scenario is not properly clear to me. Can you explain better, or give your configurations to help.

Community Member

Re: MPLS and VLANs

R1--R2--Service Provider--R3--R4 192.168.0.2

192.168.243.1 |

|

|

R5

10.10.20.4

Connectivity from R1 all the way to R4 and R5 is fine.

I'm able to ping both 10.10.20.4 and 192.168.0.2 from R1.

I'm enabling MPLS for certain subnets so I've set up an access-list so that I

can restrict which subnets will be switched through MPLS.

What is happening is that as soon as I add 10.10.20.4, 192.168.0.2 and

192.168.243.1 to this access-list, labels are generated for them on all the

routers and they are advertised as is expected. If I log into R1 and do 'show

mpls forwarding-table 10.10.20.4' I see that it has the label for R2, if I do

the same thing for 192.168.0.2 I can see that the labels are propagating as

is expected on all the routers.

If I do a ping and traceroute from 10.10.20.4 to 192.168.0.2 I can see the

MPLS labels in the output. The problem comes in however when I try and

communicate from R5 to R1 using 10.10.20.4 and 192.168.243.1. There's simply

no communication, traceroutes and pings just get timed out.

There seems to be some problem on the link between R2 and R3. R3 has no

problem forwarding traffic to R4 but traffic going to R1 doesn't seem to get

through. On R2 the command 'sh mpls forwarding-table 10.10.20.4' shows zero

bytes label switched. On R3 the command 'sh mpls forwarding-table

192.168.243.1' shows several bytes label switched.

The traffic between R3 and R2 gets tagged at the Service Provider and

delivered to a subinterface on R2, but the traffic going to R3 is untagged at

the Service Provider and delivered as is to R3. I'm suspecting that this is

the problem.

Community Member

Re: MPLS and VLANs

Sorry my message got re-formatted. Here's the diagram:

192.168.243.1

R1

|

R2

|

Service Provider

|

R3 - R5 10.10.20.4

|

R4

192.168.0.2

Silver

Re: MPLS and VLANs

Can you post the show ip route and the show mpls forwarding table for the various routers.

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