Forwarding Adjacency Scalability

Chapter 5 covered the basic configuration of forwarding adjacency, along with why you might want to use it. But you need to be careful. Forwarding adjacency in a network with a large number of LSPs can grow pretty quickly.

The increase in the number of LSPs is because of the fact that every LSP that has forwarding adjacency enabled is advertised into the IGP as a link. If you have a full mesh of TE tunnels between 128 CRs, this means that every node in the same IGP level, which previously had to deal with fewer than 500 links in the IGP, now has to deal with an additional 16,256 (128 * 127) links, bringing the total IGP size to almost 17,000 links!

17,000 is a lot. It could easily be more than your IGP can handle. Keep this in mind as you consider deploying forwarding adjacency. You might have to deploy forwarding adjacency only where it's needed, and give up some of its optimality in the name of scalability.