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 reachability, te, sr and bier.
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.