Tag Archives: mpls

MPLS/RSVP configuration & troubleshooting #1

I would like to show how I configured my MPLS cloud with RSVP signaling in this post. This is the first post of my RSVP,MPLS/VPNs series. I will use the topology below throughout my posts. In a real world MPLS core, things may be different but this is just a lab.


I have a provider MPLS core (AS8500) and several customers A,B,C,D
with different AS numbers. Addressing is as it is depicted in the picture.

RSVP as the label distribution protocol dynamically establishes Label Switching Paths (LSP) and it is fundamental to MPLS which uses this information to create its forwarding tables. Here  I use OSPF to discover the paths, which means your network must already have a working OSPF for RSVP to function properly.

Below are the steps I have taken to configure this label distribution protocol plus MPLS on top of it. I am also sharing the problems I have experienced on the way. I still lack tons of things on these protocols and the more I learn the more I see how it is immense and not easy to digest.
We have to start somewhere, let’s begin with RSVP.

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MPLS label allocation failure

I was playing with a test MPLS network today and I saw that my LSP isn’t UP.  When I checked with the show mpls command , I have seen the following “MPLS label allocation failure” message.
Then I checked the router to troubleshoot the issue. The issue was again I forgot to enable mpls at interface level.


Once I added the “family mpls” to the interfaces, all started working fine. Then I enforced some path for my LSP and then I got the following “No route toward dest” error.

This time error was the missing mpls family on the exit interface of device. Again it worked when I fixed this error. It seems I need some time on this topic:)