intermediate system to intermediate system is a link state interior routing protocol used to
flood topology information within an mpls core. topology info consists of
loopback reachability and feature parameters used within the domain.
two routers on a link send periodic hello in order to discover each
other. when a new peer discovered, lsp database is sent out in lsp pdu.
later they just periodically list a continous portion of the lsp database in a csnp pdu
for consistency checking between the peers. when one of them got a fresh lsp, that
is sent out to the peer and acknowledged with a psnp pdu. once the lsp database changed,
a router calculates shortest path first, and fills it's routing table. on broadcast network,
the routers elect designated intermediate system which is a pseudonode
adverising an additional lsp to the topology, listing all the neighbors
on the lan, and all the peers describe itself to the dis, not to each other.
here are the captures for
everything is flooded within a single lsp (which may be fragmented if needed).
information within the lsp is hierachically organized, look for features within
the lsp's is or ip reachability tlv's subtlv sections.