From: Jonathan V Hays (jhays@jtan.com)
Date: Sat Nov 22 2003 - 12:33:10 GMT-3
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Andrew Moriarty
Sent: Saturday, November 22, 2003 6:34 AM
To: Ronald.v.Dommelen@Nobel.NL; ccielab@groupstudy.com
Subject: Re: Lab questions
A few points:
BGP and OSPF need a router-id, and both support a router-id command.
OSPF
uses it (sometimes) to choose the DR for a link. BGP uses it
(eventually) to
break ties in best-path selection. Unless you are changing this
behaviour,
why would you want to change the router id? It does show up in various
databases, so you might want to change it for better readability of a
display. I wouldn't configure a router-id command unless it was required
by
a question; and even then I'd ask the procter.
I don't think EIGRP uses router-id at all- I may be wrong on that, and
if I
am someone please correct me.
I always use the exact address/inverse mask combination, or the smallest
I
can.
net 172.16.0.3 0.0.0.0 area 0
rather than
172.16.0.3 0.0.0.3 area 0
In eigrp I always advertise only one interface at a time, using the
inverse
mask as well. This way I know exactly what I am advertising. The
passive
interface command won't hurt in that situation, but it won't help
either. I
believe both are correct.
am
========
Andrew,
Here are a few points to consider.
1. When to change the BGP router ID.
In your CCIE studies you will eventually come across the problem that in
some situations the BGP and OSPF router IDs must be identical.
Specifically there is a sort of corollary to the BGP synchronization
rule:
When the IGP in a BGP AS is OSPF, then the iBGP peer's router ID and the
OSPF ASBR's router ID must match before the iBGP peer will advertise a
given prefix.
If you are experiencing this problem one possible fix would be to change
the BGP router ID.
2. EIGRP router ID.
R1(config)#router eigrp 1
R1(config-router)#eigrp r?
router-id
R1(config-router)#eigrp r
R1(config-router)#eigrp router-id 137.10.1.1
R1(config-router)#
3. Use of exact mask in OSPF network statement.
I prefer using the interface mask. It's a good habit and I can think of
at least one specific instance where using 0.0.0.0 as a wildcard mask
will result in undesired OSPF behavior, namely the Type 5 LSA forwarding
address. See the link below for details.
http://www.groupstudy.com/archives/ccielab/200310/msg01043.html
HTH,
Jonathan
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