From: Omer Ansari (omer@xxxxxxxxxx)
Date: Wed Aug 21 2002 - 16:41:56 GMT-3
yes. and just to clarify my (and possibly other ppls) misunderstanding,
step 5 in the selection process is:
5.Prefer the path with the lowest origin type: IGP is lower than EGP,
and EGP is lower than INCOMPLETE.
and not actually the AD , which is more for which route gets into the
route table.
On Wed, 21 Aug 2002, Brian McGahan wrote:
> A side note on MED:
>
> http://www.cisco.com/warp/public/459/bgp-med.html
>
> And BTW, distance does not have anything to do with BGP best
> path selection. The BGP decision process is used to determine which
> path is best. This does not necessarily mean that best routes will make
> it to the IP routing table. Distance is part of this second decision,
> but not the first.
>
> http://www.cisco.com/warp/public/459/25.shtml
>
>
> HTH
>
> Brian McGahan, CCIE #8593
> Director of Design and Implementation
> brian@cyscoexpert.com
>
> CyscoExpert Corporation
> Internetwork Consulting & Training
> http://www.cyscoexpert.com
> Voice: 847.674.3392
> Fax: 847.674.2625
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Ademola Osindero
> Sent: Wednesday, August 21, 2002 7:43 AM
> To: Yadav, Arvind K (CAP, GECIS); VANGADASALAM,SURENDRAN
> (Non-HP-Singapore,ex4); 'Omer Ansari'
> Cc: 'ccielab@groupstudy.com'
> Subject: RE: BGP Metric
>
> Arvind,
>
> Omer's explanation is quite right. The issue of admin distance does not
>
> come into play here . Infact on going thru some old posts, I found out
> that the topic was touched in detail. The key is SYNCHRONIZATION. I
> either
> turn off synchronization or ensure the routes are synchronized.
>
> I did ensured the routes were fully synchronized and the rule was
> followed.
>
> But this leads me to another question, how do i deal with my DMZ ?
>
> Regards,
> Ademola
>
>
> At 08:18 AM 8/21/2002 -0400, Yadav, Arvind K (CAP, GECIS) wrote:
> >I think EBGP routes are always prefered over IBGP because of
> >Administrative Distance, By default med metric is set to 0 to all
> routers
> >and router always compare med by default. The
> >bgp always-compare-med will be usefull when router learns router form
> two
> >different ASs.
> >
> >Arvind
> >
> >-----Original Message-----
> >From: VANGADASALAM,SURENDRAN (Non-HP-Singapore,ex4)
> >[mailto:surendran_vangadasalam@non.hp.com]
> >Sent: Wednesday, August 21, 2002 4:42 PM
> >To: 'Omer Ansari'; 'Ademola Osindero'
> >Cc: 'ccielab@groupstudy.com'
> >Subject: RE: BGP Metric
> >
> >
> >Hi,
> > I think Omer is somehow right. The bgp always-compare-med
> should be
> >used for it to choose the lower med value. If this not done then the
> >decision process will be skipped to EBGP is better than IBGP.
> >
> >Cheers!!
> >
> >-----Original Message-----
> >From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> >Omer Ansari
> >Sent: 21 August 2002 09:09
> >To: Ademola Osindero
> >Cc: ccielab@groupstudy.com
> >Subject: Re: BGP Metric
> >
> >
> >I should have explained a little more before shooting my mouth off..
> >
> >quoting the great Mr McGahan himself!
> >
> >----
> > As Chris stated, synchronization is the first requirement in
> the
> >BGP decision process. After that, the process is as follows:
> >
> >Next-hop reachability
> >Weight
> >Local Preference
> >AS-Path (shortest)
> >Origin Code (EGP > IGP > Unknown)
> >MED
> >EBGP over iBGP routes
> >Shortest internal path
> >Router-ID (lowest)
> >
> > However, there is another criterion that is worth mentioning.
> >Default local-preference for iBGP learned routes on a Cisco router is
> >100. Although local preference is higher in the decision process than
> >EBGP over IBGP, this is not the default case. You must have a
> >local-preference greater than the default (100) to choose the iBGP
> route
> >over the EBGP route. Therefore if everything (except for the default
> >local-pref of the iBGP route) is equal for two routes up to the EBGP
> >over iBGP decision, the EBGP route will be chosen. Even though the
> iBGP
> >route has a local-pref of 100, it chooses the EBGP route. Setting the
> >iBGP route to have a local-pref of at least 101 will make it chose the
> >iBGP route first.
> >----
> >
> >hope that helps.
> >
> >On Wed, 21 Aug 2002, Omer Ansari wrote:
> >
> > > Ademola,
> > >
> > > looks like an ebgp route; AD = 20 better than IBGP right?
> > >
> > > On Mon, 19 Aug 2002, Ademola Osindero wrote:
> > >
> > > > Group,
> > > >
> > > > I thought MED is meant to take preference over internal or
> external
> >routes
> > > > but i can't see it happen in the case below. R6 prefers
> 172.16.20.2 to
> > > > 192.68.6.1 to reach network 172.16.10.0 despite the fact that the
> latter
> >as
> > > > a lower metric of 0.
> > > >
> > > > Can anyone explain this?
> > > >
> > > > r6#sh ip bgp
> > > > BGP table version is 7, local router ID is 192.168.11.1
> > > > 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
> > > > *> 172.16.1.0/24 172.16.20.2 100 0 3 i
> > > > * i 192.68.6.1 50 100 0 3 i
> > > > *> 172.16.10.0/24 172.16.20.2 100 0 3 i
> > > > * i 192.68.6.1 0 100 0 3 i
> > > >
> > > > r6#sh ip bgp 172.16.10.0
> > > > BGP routing table entry for 172.16.10.0/24, version 7
> > > > Paths: (2 available, best #1, table Default-IP-Routing-Table)
> > > > Advertised to non peer-group peers:
> > > > 192.68.6.1
> > > > 3
> > > > 172.16.20.2 from 172.16.20.2 (172.16.220.1)
> > > > Origin IGP, metric 100, localpref 100, valid, external,
> best
> > > > 3
> > > > 192.68.6.1 from 192.68.6.1 (192.68.10.2)
> > > > Origin IGP, metric 0, localpref 100, valid, internal
> > > >
> > > >
> > > > Osindero Ademola
> > > > Schlumberger Network Solutions
> > > > Tel: 234 1 261 0446 Ext 5427
> > > > Fax 234 1 262 1034
> > > > email:osindero@lagos.sns.slb.com
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