From: EA Louie (elouie@xxxxxxxxx)
Date: Mon Dec 31 2001 - 06:04:30 GMT-3
dude, you missed the obvious in this scenario - ospf is running on the
192.68 network. read those configs again, and look at the sh ip bgp nei on
p 307 (2nd edition). obviously RTF found the nexthop to RTD.
of course, i'm reading from 2ed of Halabi - check the errata for 1ed of
Halabi if that's what you're using.
-e-
----- Original Message -----
From: "Adam Quiggle" <aquiggle@nc.rr.com>
To: <ccielab@groupstudy.com>
Sent: Sunday, December 30, 2001 11:49 PM
Subject: eBGP multihop & Halabi page 300 (anyone have any better ideas?)
> Hey gang,
>
> Just fooling around with eBGP multihop on page 300 of Halabi's book.
While
> looking at Figure 10-1 on page 300 I thought about an interesting
situation
> that doesn't seem to be discussed in this section (maybe it does and I
just
> haven't gotten to it).
>
> If you look at the configurations provided on pages 301-305 you will
notice
> that the configuration of RTE is conspicuously missing. I assume that
this
> was intentional to let the reader stumble across and think through this
> problem. The most obvious problem is that using the configurations
> provided RTD and RTF will not be able to form an eBGP multihop session
> since neither router has a path to the ip address used to form the BGP
> session. This can be easily solved by one of two methods:
>
> (a) static routes on RTF and RTD
> (b) configure an IGP between RTF, RTE and RTD, thus providing the
> connectivity needed to form the BGP session.
>
> This all seems simple enough and I'm sure everyone can see that solution
> (a) would not be allowed on the CCIE lab...anyway.
>
> Everything seems merry until you start thinking about routing packets
> between AS1, AS2 and AS3. It seems that RTE would cause a lot of problems
> very quickly since it does not have a path to any of the networks in AS3
or
> AS1 (assuming that AS2 would have its own IGP that would inform it of
> routes within its own AS). In addition we can not redistribute BGP routes
> from AS1 and AS3 into the IGP of AS2 from RTD since that will just cause a
> routing loop between RTE and RTD.
>
> It seems to me that in order to solve this problem the routes for AS3 and
> AS1 must come from RTF. To solve this problem I see one of two solutions:
>
> (a) configure a default route on RTE pointed at RTF and rely on the IGP to
> inform router RTE about routes within AS2 (this means AS2 could not be a
> transit AS)
> (b) Redistribute BGP on RTF into the IGP running between RTF, RTE and RTD.
>
> Does anyone see another solution to this problem?
>
> Thanks,
> AQ
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