according to doyle:
A router originates a link-state advertisement to describe one or more destinations. An OSPF Update packet transports LSAs from one neighbor to another. Although LSAs are flooded throughout an area or OSPF domain, Update packets never leave a data link.
this is correct, but vague...
lsa's are contained in update packets that are exchanged between routers that share the same data link, but the update packets themselves never leave the link... this is the finer point..
doyle does better in his book, OSPF and IS-IS: Choosing an IGP for Large-Scale Networks:
OSPF uses an Update packet to send LSAs from one router to another during the flooding process. Whereas LSAs are flooded throughout an area, Update packets are exchanged only between directly connected routers. That is, their scope is the local link. If an LSA received in an Update packet must be forwarded to another router, it is put into a new Update packet for the next hop. This is in keeping with the fact that none of the five OSPF message types are forwarded beyond the local link.
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