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Home > Archive > CCNP > February 2001 > What makes EIGRP a Hybrid to Distance Vector and Link State Protocols?
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What makes EIGRP a Hybrid to Distance Vector and Link State Protocols?
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| Evenflow 2001-02-15, 7:17 pm |
| I know EIGRP is classified as a Hybrid protocol and uses both Distance Vector and Link State protocol features but what exactly are its Distance Vector Features? Looks like it just converts with IGRP
It looks more like a Link State to me :-)
Can anyone tell me the Distance Vector features?
Thanks
-Evem | |
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| An EIGRP router sends (parts of) its routing table to adjacent routers, as per DV protocols.
It does so when a change in its routing table occurs, as per LS protocols.
There's probably more than this.
HTH | |
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| Dmaftei,
In a pure distance vector enviornment, the routing update includes a complete routing table.
EIGRP does not send periodic updates. Instead, it uses partial updates when a path or the metric to a destination changes. DUAL sends an update about only that link rather than the entire routing table. The information is passed only to routers that require it, in contrast to link-state protocols operation, which sends a change upddate to all routers withen an area.
I just read all that and it still is a bit confusing as to the reasoning of EIGRP being a Distance Vector protocol
Thanks
Even | |
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| Here is the awnser to my question I think.
Please tell me if I'm wrong though.
EIGRP has these Distance Vector Features
Split Horizon.
Triggered updates with route posioning.
Thanks
Even | |
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| quote:
Originally posted by Evenflow
EIGRP has these Distance Vector Features
Split Horizon.
Triggered updates with route posioning.
Split horizon is not a feature; it's a hack invented to solve a problem inherent in DV protocols (the count to infinity problem). Triggered updates and route poisoning are not features either; they are improvements meant to speed the convergence. (Well, I guess you could name them features, but I'm referring to things that are inherent to the protocol. DV protocols can function without these "features").
The characteristic of DV protocols is that routers send their routing tables to adjacent routers. They do so at regular intervals (i.e. on timers). The knowledge base of a router is restricted to itself and the adjacent routers (it knows its cost to reach its neighbors, and knows the neighbors' routing tables). A router has no idea what routers two or more hops away know. The information exchanged is "these are all the subnets I can reach". In this respect EIGRP behaves like a DV protocol.
On the other hand, routers in LS domains know the picture of the whole domain. That's because link state updates are flooded throughout the domain. Therefore each router knows about every other router. The information exchanged is "these are my links". When the state of one link changes, the affected router sends out the new "state of its links", and all the other routers learn about the change. EIGRP sends updates when something changes; in this respect it behaves like a LS protocol.
Makes sense? |
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