It’s been a while since I am asking this question in interviews
to Routing & Switching candidates that comes from different background like
Enterprise and Service Provider and certification level like CCNP, CCIP, CCIE
etc.
Yet again I asked same question
to couple of people I was interviewing today that had same thoughts as well of
EIGRP being Hybrid.
Okay let’s forget the word “Interview” :) and
focus on flip side which is that many of our own customers runs EIGRP as IGP in
their networks and probably they may ask you similar questions or might have
same thought process
Usually when I ask this question the answers comes as “Hybrid”.
And of course then I ask people how is it “Hybrid ?” and people start
explaining that It has some features of Distance Vector Protocol and some it
borrow from Link state.
And then I ask them again – What are those features that you
think it borrows from Link state ?
And usually people replies back as – Hey , It has Topology
Table, Routing updates are triggered , neighbor discovery and bla bla bla which
comes from Link State background
Now of course one must first understand the differences in terms
of EIGRP topology table Vs OSPF Topology Table per say to begin with.
EIGRP has no clue what’s there beyond its connected neighbor.
Where in OSPF every router knows about entire topology.
Similarly EIGRP updates don’t go beyond immediate neighbor
whereas in Link State (OSPF) every router in area gets the same copy of LSAs
and pass them to neighbors without any modification.
Each router in ospf within same area has same LSDB and runs
independent SPF calculation whereas EIGRP router just passes the best routes to
its neighbor which that neighbor further stores into Topology table and run
DUAL to figure out best path.
So perhaps we can call EIGRP as advance distance vector but
definitely not Hybrid. And one reason that myth might have become popular
because of is many Cisco Press Routing focused books using “Hybrid” terminology
for EIGRP.
HTH...
Deepak Arora
Evil CCIE
6 comments:
Agreed. Also forming adjacency is not necessarily a quality of a link-state protocol.
And while we're at it... let's just say that BGP is not a "path-vector" but simply a distance-vector one too.
Agreed. Also forming adjacency is not necessarily a quality of a link-state protocol.
And while we're at it... let's just say that BGP is not a "path-vector" but simply a distance-vector one too.
According to you. For years I teach Cisco courses, and always prefer to say that EIGRP is Advanced Distance Vector and isn't a Hybrid protocol. It is more accurate.
According to you. For years I teach Cisco courses, and always prefer to say that EIGRP is Advanced Distance Vector and isn't a Hybrid. It is more accurate.
Eigrp is more distance vector than a distance vector routing protocol ;) ;)
Eigrp had to implement a not so well taught query/reply mecasim to avoid periodical full routes updates. Yes, this has advantages but brings also issues such as SIA and huge quer/reply propagation domain in big scale implementations.
It is the fastest IGP though. And unequal load sharing is cool.
Composite metric is a joke however.
Jad.
@ Pera
From chapter 6 (Understanding EIGRP) of Troubleshooting IP Routing Protocols I read this:
“EIGRP is neither a classic distance vector routing protocol nor a link-state protocol—it is a hybrid of these two classes of routing protocol. Like a distance vector protocol, EIGRP gets its update from its neighbors. Like a link-state protocol, it keeps a topology table of the advertised routes and uses the Diffusing Update Algorithm (DUAL) to select a loop-free path.”
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