Link State Protocols

[jacquesd]

Hi All,

Am I correct in saying that link state protocols (including EIGRP) ONLY send topology information to their neighbors in terms of routing updates. No specific routes are sent like in RIP etc. The protocols run SPF or DUAL on the topology database to find the routes they deem the best. When the topology changes (link goes down etc), the directly connected router will send the new topology info to it's neighbors.

Tx

Jacques

[ruwhite]

Not entirely.... You have to separate the mechanism used to report topology changes to a neighbor from the mechanism used to calculate the best path to any given destination in the network.

-- EIGRP is a distance vector protocol, based on DUAL, that uses incremental updates.

-- RIPv2 is a distance vector protocol, based on the Belman-Ford algorithm, that uses incremental and periodic updates.

-- BGP is a path vector protocol that uses incremental updates.

-- OSPF is a link state protocol that relies on Dijkstra, and uses incremental updates plus periodic reflooding (prediodic updates) for validity checking.

-- IS-IS is a link state protocol that relies on Dijkstra and uses incremental updates plus periodic reflooding (periodic updates) for validity checking.

In fact, there have been link state protocols in the past that relied entirely on periodic updates, rather than incremental updates. So the two are separate things, really.

:-)

Russ

[jacquesd]

Yes, I suppose my statement is a bit too general. There is too many protocols and they do not function in the same way. I am trying to understand the link state process a bit better in what exactly is actually being exchanged between neighbors. I suppose reading a OSPF or the like white paper won't hurt :)

Tx

Jacques

[ruwhite]

http://www.cisco.com/en/US/tech/tk365/tk207/technologies_white_paper09186a0080094cb7.shtml

is a good place to start for EIGRP. The little EIGRP book on Addison-Weseley is a good start, as well, and not so expensive (I think it ususually sells for under $20). For link state protocols, I'd actually start with the IS_IS book out on Addison-Wesley, and then look at the OSPF book on Cisco Press.

:-)

Russ.W