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MPLS tunneling in SROS

July 8, 2013 3 comments

I wrote this post ages ago but I have been putting all my time in to CCIE SP labbing and work has been mental so no time for dossing.

Next up I want to look at the basics of MPLS and RSVP configuration. This is an expansive topic and provides a huge amount of flexibility in what you want to achieve with it. This post will cover the basics of setting up interfaces, configuring paths and LSPs.

Let’s get started!

First off we need to know that MPLS and RSVP have a large dependency on each other. Signalling for MPLS tunnels requires RSVP for the path/resv message propagation. We need to configure our interfaces in to the MPLS process and then enable it. Creating an interface in the MPLS context also places it in RSVP, the only thing we need to do is unshut RSVP.

I already have these protocols running so enabling them wont impact anything, it’s simple to configure though

config router mpls no shut

config router rsvp no shut

Below we see how to add an interface in and that it is placed in to RSVP automatically. By simply creating the interface in MPLS we are capable of originating, transiting and terminating LSPs.

enable mpls int

Once we enable this at all interfaces in the network then we are good to go for end to end LSPs.  If you don’t enable it on all interfaces then your tunnels may fail to come up, or worse fail in a live environment should there be some convergence. Next let’s create a path from r5 to r1. For now we will create it as a loose path with a single hop to the system address of r1.

loose pth

Now we need to create the LSP and bind the path to it. We will also enable cspf for future use. This allows the use of constraints to be placed against the LSP such as affinities, SRLG.  We need to configure the ‘to’ address as the same as the ultimate endpoint of the path.  ‘primary’ gives us the ability to assign the path as the preferred path.  You can also assign a ‘secondary’, or multiple secondaries, to the LSP but there isnt much point when using loose paths and no constraints.  Maybe just in case you shut down the primary path by mistake.

loose lsp

As we can see from the above screenshot the LSP is now up, only in one direction of course.  We have an equivalent path in the opposite direction.  Lets have a look at the best troubleshooting command you can use for this, well in my experience.

lsp detail

So above we can see the path the LSP is actually taking in the network goes through r5’s egress interface to r3, r3 ingress from r5 and then terminates at r1.  We can also see the labels that have been allocated to the tunnel.  If there is an @ beside a hop that means there is a detour available which changes to a # when the detour is in use.

If you want to see the detour path that will be further down the detailed information:

standby lsp

The DetourAvoid will show the interface you must not transit and everything is done automatically, no need to manually build detours yourself.

That’s all I got on this, gotta get back on the Ciscos… Next I will be looking at affinities and how you can control your forwarding path with link colouring, cos that’s kinda cool.

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Categories: ALU MPLS