I expect there to be many excellent responses to this, but I'll start off
with a mediocre one. :-)
Distance vector and link state routing protocols primarily differ in three
ways: how they notify their neighbors of the routes they know about, how
they go about building their own routing table out of that information, and
how they notify neighbors of changes.
A DV protocol, like RIP or EIGRP, send their entire routing table to their
directly attached neighbors and then receive their neighbors routing tables
in return. That's an important point: they send the *entire* routing table,
not just the routes they know about first hand.
Based on their own information and the tables received from neighbors, they
build a routing table that basically says "I have <some route>, and it's
<some distance> away, and it's that direction (vector)." Hence the name,
distance vector. RIP uses hop count as its metric, so a RIP routing table
says "x.x.x.x is out that interface and it's Y hops away." EIGRP has a more
complex metric but the end result in the routing table is similar.
Now, link state protocols are quite different. They don't just haphazardly
deluge each attached link with their entire routing tables, they do it in a
little more organized fashion. Let's take OSPF as an example.
An OSPF router will send advertisements to its neighbors about the routes
or, more specifically, links that it's personally aware of. These
advertisements get flooded throughout the area and all involved routers use
those advertisements to construct a picture of the entire topology of the
network. This is quite different behavior from DV protocols. They simply
know direction and distance, but they don't have a big picture view of the
entire network layout.
A router running OSPF will have a complete understanding of its place in the
network topology, and it builds its routing table by choosing the
lowest-cost path to each other router in its area based on the link state
information it received from its neighbors.
Now, about updates; DV protocols handle these quite differently than LS
protocols. RIP and IGRP periodically send their entire routing table, even
if no change has occurred. EIGRP initially sends its entire table, but then
sends incremental updates as changes occur.
OSPF, once it has completely synchronized with its neighbors, will only send
incremental updates as needed.
This has been quite on over-simplification of the topic, but I hope that
helps out a little bit. There will be other more complete and accurate
responses that will give more details and probably be more intelligible.
<g>
Regards,
John
> Hi
>
> I just a general question about routing protocols, if anyone could
help
> me out here I'd be grateful.
> When comparing EIGRP to Distance Vector routing protocols, like RIP,
> the only similarity that I noticed was that the network statements are
both
> classful. Is this the only characteristic that prevent EIGRP from being
> considered a total link-state routing protocol? Or is there something
else I
> failed to notice?
>
>
> Thanks in Advance,
> Freddy Krugar III
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