There is a meaning common to all routing protocols, and an additional
special meaning in BGP.
A peer is a router with which you have a direct IP connection. In
other words, two BGP routers are peers as long as the BGP connection
is between the loopbacks on both routers; there can be intervening
IGP routers.
Peer implies neighbor, but, in some protocols, has the additional
nuance that you exchange routing information with it as well as
forward through it.
As a rule of thumb, you should not have more than 20-30 iBGP or eBGP
peers on a BGP router, unless you know exactly what you are doing and
can do the appropriate capacity planning.
This is a reasonable rule for IGP routers as well, with the caveat
that you can have more static peers than that. The total number of
peers are limited by the number of Interface Descriptor Blocks that
are available. IDBs are the sum of all logical and physical
interfaces, including subinterfaces. For a long time, it was 300,
but newer releases allow more.
The 50 router limit per OSPF area is conservative, but it doesn't
refer to peers, but the total number of OSPF routers in the area. The
reason for this is the workload for computing the Dijkstra, in a
single area, is proportional to:
((numberOfPrefixes * numberOfPrefixes) * log(numberOfRouters)
So the more total routers (i.e., Type 1 LSAs), the more the CPU load
goes up. Still, an experienced designer may be able to get hundreds
of routers working in an area, although they may need fast CPUs.
I wouldn't want to have more than a maximum of 47 OSPF routers on the
same segment, since that's the maximum you can fit into a single
Hello packet.
Someone mentioned limits of peers per AS. Certainly, if that's in
the BGP sense, large providers routinely have thousands, perhaps tens
of thousands, of routers. They certainly use hierarchy and don't put
excessive peers on any given box.
--
"What Problem are you trying to solve?"
***send Cisco questions to the list, so all can benefit -- not
directly to me***
********************************************************************************
Howard C. Berkowitz [EMAIL PROTECTED]
Chief Technology Officer, GettLab/Gett Communications
Technical Director, CertificationZone.com
"retired" Certified Cisco Systems Instructor (CID) #93005
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=35817&t=35705
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