From: Darren Hosking (dhosking@xxxxxxxxxxxxxxxx)
Date: Mon May 21 2001 - 10:25:57 GMT-3
I cleared the IBGP AS and I did see WITHDRAWN updates coming through on the
router with higher local preference (didn't see the other router sending
them - used debug ip bgp update). So if the link to the ISP via r1 with
higher local preference goes down, IBGP will update this router (r1) with
the routes from r2? Are these routes requested by one router or sent by the
other?
Thanks, Darren
Configs are as follows:
r1 (primary link):
router bgp 65000
no synchronization
bgp log-neighbor-changes
neighbor 10.0.1.1 remote-as 1221
neighbor 10.0.1.1 ebgp-multihop 255
neighbor 10.0.1.1 route-map SET_OUTBOUND_TRAFFIC in
neighbor 10.0.1.1 filter-list 10 out
neighbor 172.24.96.1 remote-as 65000
neighbor 172.24.96.1 next-hop-self
ip as-path access-list 10 permit ^$
route-map SET_OUTBOUND_TRAFFIC permit 10
set local-preference 300
r2 (backup link):
router bgp 65000
no synchronization
bgp log-neighbor-changes
neighbor 10.0.2.1 remote-as 1221
neighbor 10.0.2.1 route-map SET_OUTBOUND_TRAFFIC in
neighbor 10.0.2.1 filter-list 10 out
neighbor 172.24.24.1 remote-as 65000
neighbor 172.24.24.1 next-hop-self
ip as-path access-list 10 permit ^$
route-map SET_OUTBOUND_TRAFFIC permit 20
set local-preference 250
-----Original Message-----
From: mcaplan.cs@clearstream.com [mailto:mcaplan.cs@clearstream.com]
Sent: Monday, 21 May 2001 7:07:PM
To: dhosking@commander.com.au; ccielab@groupstudy.com;
zhutong@ronghai.com.cn
Subject: RE: should all IBGP neighbours have all EBGP paths?
Darren,
I cant tell without diagrams and configs, but I suspect its a case of BGP
only advertises the best path.
Consider the following example
r3----------------r4 AS2
| |
++++++++++++++++++++++
| |
| |
r1-----------------r2 AS1
If R2 has the better local preference to AS2, it will tell R1 about it. R1
will then decide that R2 is the best route to AS2. Any route that R1 had
advertised to R2 as a route to AS2 will be then withdrawn. If you use 'debug
ip bgp updates' you can actually see this WITHDRAWN message being sent.
After that R2 will only have a single route to AS2 in the BGP table. R1
however will probably have 2 routes in its BGP table - the best one via R2
and the other via R3.
Hope this helps
Mark
> ----------
> From: zhutong[SMTP:zhutong@ronghai.com.cn]
> Reply To: zhutong
> Sent: Montag, 21. Mai 2001 08:02
> To: Darren Hosking; ccielab@groupstudy.com
> Subject: Re: should all IBGP neighbours have all EBGP paths?
>
> Give your config pls.
>
> ----- Original Message -----
> From: "Darren Hosking" <dhosking@commander.com.au>
> To: <ccielab@groupstudy.com>
> Sent: Monday, May 21, 2001 11:44 AM
> Subject: should all IBGP neighbours have all EBGP paths?
>
>
> > I have 2 BGP routers connected externally to the same AS and internally
> to
> > each other using IBGP. The local preference is set to prefer one link
> over
> > the other. All paths are visible on the non-preferred router (shows both
> > paths out with the other as preferred), however, the router with the
> > preferred path to the ISP only shows the paths it knows about and not
> the
> > paths via the other link.
> >
> > Is this correct? Don't both need all paths or are they exchanged when
> the
> > preferred path is no longer available (could be a lot of traffic)?
> >
> > I'm using Halabi 1st edition as reference, is the 2nd edition much
> better
> > and in what areas (ie should I buy the newer edition).
> >
> > Thanks, Darren
> >
> > The output of sh ip bgp summ and sh ip bgp for one network is shown
> below.
> >
> > Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down
> > State/PfxRcd
> > 10.0.1.1 4 1221 6221 3628 43815 0 0 2d12h
> 6606
> > 172.24.24.1 4 65000 6626 6313 43815 0 0 13:10:59
> 6606
> >
> > BGP table version is 43789, local router ID is 172.24.97.1
> > 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
> > *>i9.3.4.0/24 172.24.24.1 300 0 1221 ?
> > * 10.0.1.1 250 0 1221 ?
> >
> > Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down
> > State/PfxRcd
> > 10.0.2.1 4 1221 43026 26728 37714 0 0 4d01h
> 6605
> > 172.24.96.1 4 65000 11860 12348 37714 0 0 13:10:26
> 0
> > <---?????
> >
> > BGP table version is 37689, local router ID is 172.24.23.1
> > 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
> > *> 9.3.4.0/24 10.0.2.1 300 0 1221 ?
> > **Please read:http://www.groupstudy.com/list/posting.html
> **Please read:http://www.groupstudy.com/list/posting.html
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