From: Carlos G Mendioroz (tron@xxxxxxxxxxx)
Date: Mon Jun 24 2002 - 14:36:59 GMT-3
How ?
Serguei, for those of us without Doyle, would you please copy the
details ?
I think this has more to do with the "maximum-path" than with the
multiaccess
media between RTD & RTA.
Somehow, RTA wants to "use" many paths to the 172.17.1.0/24, and the
only
way it has is to say "let me do it" by doing something like
"next-hop-self".
If you take the maximum-path away, you'll revert to standard 10.1.1.2
nexh hop.
HTH,
"Bezverkhi, Serguei" wrote:
>
> On multi-access media BGP next hop behavior is different. It is well
> explained in Doyle's book.
>
> Serguei
>
> -----Original Message-----
> From: Hunt Lee [mailto:ciscoforme3@yahoo.com.au]
> Sent: June 22, 2002 9:07 PM
> To: ccielab@groupstudy.com
> Subject: BGP Next-Hop attribute
>
> Sorry, the bgp output stuffs up before, so here's a repost ;)
>
> Hey all, I'm probably missing some fairly simple concept here. I have
> setup 4 routers as follows:-
>
> RTB
> /
> RTD --- RTA
> \
> RTC
>
> Both RTB & RTC are connected (via Eth) to a network called
> 172.17.1.0/24. RTA & RTD are both in AS2 RTB & RTC are both in AS1
>
> The connection between RTA & RTD is via Ethernet
>
> RouterA#sh ip bgp
> BGP table version is 9, local router ID is 25.25.25.2
> Status codes: s suppressed, d damped, h history, * valid, > best,i
> -internal
> Origin codes: i - IGP, e - EGP, ? - incomplete
> Network Next Hop Metric LocPrf Weight Path
> *> 10.1.1.0/30 10.1.1.2 0 0 1 i
> * 10.1.2.2 0 1 i
> *> 10.1.2.0/30 10.1.1.2 0 1 i
> * 10.1.2.2 0 0 1 i
> *> 25.25.25.0/24 0.0.0.0 0 32768 i
> *> 172.17.1.0/24 10.1.1.2 0 0 1 i
> * 10.1.2.2 0 0 1 i
>
> RouterA#sh running-config
>
> router bgp 2
> network 25.25.25.0 mask 255.255.255.0
> neighbor 10.1.1.2 remote-as 1
> neighbor 10.1.2.2 remote-as 1
> neighbor 25.25.25.1 remote-as 2
> maximum-paths 6
>
> When I lookup RTD's BGP table (shown below), for the route
> 172.17.1.0/24,
> instead of via 10.1.1.2 or 10.1.2.2, it is 25.25.25.2. Ok - here's
> what I'm
> confused about. Since I thought that in EBGP peering, the next hop is
> usually
> the IP address of the neighbor that announced the route, but IBGP
> peering
> preserve the Next-hop attribute learned from EBGP peers. So in the
> case, if I
> haven't use next-hop-self on RTA, I would think the EBGP next hop in
> RTD's BGP
> table would be either 10.1.1.2 or 10.1.2.2, but why is the EBGP
> next-hop is
> 25.25.25.2?
>
> RouterD#sh ip bgp
> BGP table version is 6, local router ID is 172.16.0.2
> Status codes: s suppressed, d damped, h history, * valid, >
> best,i-internal
> Origin codes: i - IGP, e - EGP, ? - incomplete
> Network Next Hop Metric LocPrf Weight Path
> *>i10.1.1.0/30 25.25.25.2 0 100 0 1
> i*>i10.1.2.0/30 25.25.25.2 100 0 1
> i*>i25.25.25.0/24 25.25.25.2 0 100 0 1 i
> *>i172.17.1.0/24 25.25.25.2 0 100 0 1 i
>
> Thanks,
>
> H.
>
> http://www.sold.com.au - SOLD.com.au
> - Find yourself a bargain!
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