OSFP Forwarding Address Part I: Type 5 LSA Suppression
OSPF (Open Shortest Path First) is mostly seen as a pretty nasty routing protocol, with a load of subtleties and corner cases. I’ve decided to talk about a subject which usually gives a lot of troubles to most network professionals – the Forwarding Address (FA).
So, we’re going to clear things on why does OSPF set or doesn’t set the FA, what is it used for, how is the best path selection is influenced by the setting of the FA and we’ll also see some examples that may throw some light on this subject. But first, let’s clarify what the forward address is. As per the RFC, the forward address is defined as:
Forwarding address Data traffic for the advertised destination will be forwarded to this address. If the Forwarding address is set to 0.0.0.0, data traffic will be forwarded instead to the LSA's originator (i.e., the responsible AS boundary router).
Probably the most important thing when you start the deep dive into this subject is having the right topology to work with, which allows you to see the less usual cases regarding how redistribution into OSPF works.
Considering the network topology below, I have Continue reading