Alcatel Unleashed

Hi,

I am a bit confused why my configuration does not work. Topology is attached.

I shutdown port between R1, and R2, and configure R6 as loose hop, and now when I try to ping router R4 from R6 it does not work. I am wondering why it does not work? I do not save the config so I can not paste it here, but maybe you highlighted the most common mistakes during configuration strict and loose hops for RSVP, and LDP?

Regards.

So when you run LDP, all you need to do is insert each interface into the interface-parameters context of the CLI. So something like:

configure router ldp interface-parameters interface <interface-name>

This will turn on LDP as transport, also known as link LDP, so that you will build LSP's automatically. Essentially this would equate to RSVP Path's that contain nothing but loose hops, just no control over things like bandwidth, link include/exlude and the like.

Now, RSVP requires paths to be built to traverse the network. In the case of your diagram, lets say we are building an LSP that goes from R4-->R6 with the assumption that OSPF is your IRP. You can build an LSP in this case to follow any number of paths that will get from R4-->R6, some will just be redundant, or you might want FFR for protection, whatever. I will show a couple here an explain the differences.

Example 1:
This will go from R4>R3>R1>R2>R6.

configure router mpls path "doobie"
hop 1 [sys ip R3] strict
hop 2 [sys ip R1] strict
hop 3 [sys ip R2] strict
hop 4 [sys ip R6] strict

Should you have any topology changes then this Path will die and take any LSP with it unless there is protection from FFR or Secondary Paths.

Example 2:
This will go from R4-->R6.

configure router mpls path "doobie-loose"
hop 1 [sys ip R6] loose

Now this path will still get an LSP to R6, but only follow routing to your destination instead of specific hops, and provided you are running OSPF or ISIS, will recover from any topology change you may enounter without need for FFR/Secondary Paths, but slower since it needs OSPF/ISIS to recover first before the Path can. I would still recommend FFR or Secondary Paths.

Now it can get a bit crazy. Let's say you wanted to go from R4-->R6 and do some traffic engineering. If you were to follow the "doobie-loose" path from above, your traffic will go from R4>R2>R6, and the "doobie" path is from R4>R3>R1>R2>R6. Notice in either case, assuming things in the network are running as expected, no matter what path you use the traffic will end up going through the link from R2-R6.

You could do something like this:

configure router mpls path "doobie2"
hop 1 [sys ip R1] loose
hop 2 [sys ip R6] loose

This will keep you from explicitly dictating hops, allow OSPF/ISIS to choose the best path from R4 to R1 and make sure that you don't go over the link from R2>R6.

There are many different ways to set this up. It depends on what you need the LSP to do, how it needs to traverse the network, and what protection you need.

Hope this helps.