Eigrp is a hybrid as it have some characteristics of DV & Link state.
DV = limited hop count
Linkstate= 3 tables routing, topology,nei + keep nei relationship + hellos
Also trust me in this, DV protocols add the metric and then send the update to the nei router, the nei router just put teh update in his routing table.
BUT in Hybrid, the router send its own metric that resides in its routing table , and send this message to the nei, The nei will check the message AND ADD HIS OWN METRIC, and here comes the hybrid protocol with the FD & RD/AD
SO Eigrp is a hybrid protocol, if that didn't convince you name it an advanced DV.....trust me it wont make a network outage.
EIGRP has nothing to do with hybrid protocol. The only hybrid protocol commonly used is the multi-area OSPF.
Look, We have to look on a defining property of a protocol, on the fundamental principle on which it operates, and that shall be the decisive thing that tells us what is a LS and what is a DV. Looking on the supporting mechanisms is just looking plain wrong.
We call protocols distance-vector or link-state if they fulfill a certain architectural criteria.
Now, a link-state protocol must work on this basis:
1.) Each router describes in detail its connections to the neighboring objects (routers, networks)
2.) This information is flooded without any change to all routers in an area
3.) Each router consequently has information about all routers, all networks and their detailed interconnections, and from this table, the entire network topology can be drawn
4.) Each router calculates the shortest paths on its own using the topology map
A distance-vector protocol operates by sending a list (an array = a vector) of known networks and their individual metrics. That's about it.
Now, a hybrid protocol is a protocol that represents a network in part by link-state approach and in part by distance-vector approach.
The EIGRP does not do anything similar.
Adding lengths is not a link-state thing, nor is maintaining a feasible distance for a destination. Actually, Dr. Jose Joaquin Garcia-Luna-Aceves, the author of the DUAL, devised the entire DUAL including the feasible distance and the feasibility condition WITHOUT ANY ASSUMPTIONS with regards to DV or LS routing protocols.
The goal of DUAL was actually to avoid having a link-state database to avoid routing loops. If you have a link-state database, the Dijkstra algorithm guarantees by itself that it will not create routing loops. But Dr. Garcia wanted to improve the DV protocols with a supporting conditions how to avoid routing loops without knowing more about the network topology.
Actually, the EIGRP works with the same knowledge about the network as RIP has, it just tries to remember more information about the distance dynamics and it uses some sufficient conditions (the mathematical proofs of which are nontrivial) to be sure that the routing loop will not be created even without knowing how the network looks like.
I hope, It is clear to you now.
Edited by Mr.Mandeep, 26 December 2009 - 08:00 AM.