From: Volkov, Dmitry (Toronto - BCE) (dmitry_volkov@xxxxxxxxx)
Date: Mon Jun 24 2002 - 15:49:04 GMT-3
It's here:
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ics/icsbgp4.htm#xtocid20439
17
http://www.cisco.com/warp/public/459/14.html#A13.0
Dmitry
-----Original Message-----
From: Bezverkhi, Serguei [mailto:Serguei.Bezverkhi@hp.com]
Sent: Monday, June 24, 2002 2:07 PM
To: Carlos G Mendioroz
Cc: ccielab@groupstudy.com
Subject: RE: BGP Next-Hop attribute
Could not find it fast in Doyle, but here is the explanation from Cisco
Web site:
Q. In eBGP sessions, which IP address is sent as the next hop?
A. In eBGP peering, the next hop is the IP address of the neighbor that
announced the route. However, when the route is advertised on a
multi-access media (such as Ethernet or Frame Relay), the next hop is
usually the IP address of the router interface connected to that media,
which originated the route. For a more detailed explanation, please
refer to BGP Nexthop Attribute.
Hope this helps
Serguei
-----Original Message-----
From: Carlos G Mendioroz [mailto:tron@huapi.ba.ar]
Sent: June 24, 2002 1:37 PM
To: Bezverkhi, Serguei
Cc: Hunt Lee; ccielab@groupstudy.com
Subject: Re: BGP Next-Hop attribute
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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