From: ying chang (ying_c@xxxxxxxxxxx)
Date: Sat Apr 06 2002 - 20:07:10 GMT-3
Greg,
That's what we thought. But in this case, the MED comparision will always be
skipped, because one of the neighbor is reside in the same AS. Please see my
other post which includes my config and output. There's no problems in
Halabi's book pg 337-340 or Doyle II's pg pg 107-108 examples. The question
is what does router do when it learns the same route from both ebgp and
ibgp. From what I've seen so far, no problems when it learns the route from
ebgps, and no problems when it learns the router ibgp, but it seems it will
not compare MED if the route is learned from both ebgp and ibgp.
I'm confused as usual...
Thanks,
Chang
>From: Greg Parrish <gparrish@yahoo.com>
>Reply-To: Greg Parrish <gparrish@yahoo.com>
>To: ying chang <ying_c@hotmail.com>
>CC: dan_schaw@yahoo.com, jgraun@attbi.com, pdostal@724.com,
>ccielab@groupstudy.com
>Subject: Re: BGP MED - again
>Date: Sat, 06 Apr 2002 17:10:21 -0500
>
>If you want to influence the route when leaving R3 then use a route map to
>change the local pref on the learned route from R1/R2. If you want to
>influence
>R1/R2 on which way they will come in then modify the MED. This is what I
>know,
>let me know if someone disagrees.
>
>Thanks,
>Greg
>
>
>
>
>ying chang wrote:
>
> > Well, "bgp always compared Med" would not work help in this case as they
> > both come from AS1.
> >
> > There are two web pages are helpful:
> >
> > http://www.cisco.com/warp/public/459/bgp-med.html
> > http://www.cisco.com/warp/public/459/37.html
> >
> > Here's my question, if we stick on the original problem, which is we are
> > trying to tell AS1 to prefer R1-R3 route instead of R2-R3 route, how can
>we
> > do it without changing anything on either R1 or R2? Can it be done? In
> > simple term, R1 and R2 are proctor's routers, and you have to work on R3
>to
> > make R1 and R2 always prefer R1-R3 route.
> >
> > Thanks,
> > Chang
> >
> > >From: Muhamamd Durrani <dan_schaw@yahoo.com>
> > >Reply-To: Muhamamd Durrani <dan_schaw@yahoo.com>
> > >To: Jason <jgraun@attbi.com>, "'Peter Dostal'" <pdostal@724.com>,
> > >ccielab@groupstudy.com
> > >Subject: RE: BGP MED
> > >Date: Fri, 5 Apr 2002 23:00:57 -0800 (PST)
> > >
> > >you should use "bgp always compared Med " command to
> > >force BGP to compare MED for destination from
> > >Different AS systems . By default BGP donot compare
> > >MED for same destinations from neighbors from
> > >different AS.
> > >
> > >So R2 must have this command and than verify ur result
> > >....
> > >
> > >Regards,
> > >Muhammad
> > >
> > >
> > >--- Jason <jgraun@attbi.com> wrote:
> > > > Well iBGP as an Admin distance of 200 while eBGP has
> > > > an admin distance
> > > > of 20
> > > >
> > > > -----Original Message-----
> > > > From: nobody@groupstudy.com
> > > > [mailto:nobody@groupstudy.com] On Behalf Of
> > > > Peter Dostal
> > > > Sent: Friday, April 05, 2002 6:58 PM
> > > > To: ccielab@groupstudy.com
> > > > Subject: BGP MED
> > > >
> > > > I have a problem with BGP path selection process.
> > > > Based on the BGP path
> > > > selection process I would say that router R2 should
> > > > choose iBGP path
> > > > over
> > > > eBGP (because of lower MED). Any suggestions?
> > > > Thanks,
> > > >
> > > > Peter
> > > >
> > > >
> > > > R1----FrameRelay----R2
> > > > | |
> > > > ------Ethernet-------
> > > > |
> > > > R3
> > > >
> > > > *********************************************
> > > > hostname R1
> > > > !
> > > > interface FastEthernet1/1
> > > > ip address 192.168.2.3 255.255.255.0
> > > > !
> > > > interface Serial1/0
> > > > ip address 192.168.1.1 255.255.255.0
> > > > encapsulation frame-relay
> > > > no keepalive
> > > > no fair-queue
> > > > frame-relay interface-dlci 100
> > > > !
> > > > router bgp 2
> > > > bgp log-neighbor-changes
> > > > neighbor 192.168.1.2 remote-as 2
> > > > neighbor 192.168.1.2 next-hop-self
> > > > neighbor 192.168.2.1 remote-as 1
> > > > neighbor 192.168.2.1 route-map BGP_MAP in
> > > > no auto-summary
> > > > !
> > > > route-map BGP_MAP permit 10
> > > > set local-preference 100
> > > >
> > > > *********************************************
> > > > hostname R2
> > > > !
> > > > interface FastEthernet0/0
> > > > ip address 192.168.2.2 255.255.255.0
> > > > !
> > > > interface Serial0/0
> > > > ip address 192.168.1.2 255.255.255.252
> > > > encapsulation frame-relay
> > > > no keepalive
> > > > no fair-queue
> > > > frame-relay interface-dlci 100
> > > > !
> > > > router bgp 2
> > > > bgp log-neighbor-changes
> > > > neighbor 192.168.1.1 remote-as 2
> > > > neighbor 192.168.1.1 next-hop-self
> > > > neighbor 192.168.2.1 remote-as 1
> > > > neighbor 192.168.2.1 route-map BGP_MAP in
> > > > no auto-summary
> > > > !
> > > > route-map BGP_MAP permit 10
> > > > set local-preference 100
> > > > !
> > > > *********************************************
> > > > hostname R3
> > > > !
> > > > interface FastEthernet0/1
> > > > ip address 192.168.2.1 255.255.255.0
> > > > !
> > > > interface Loopback0
> > > > ip address 170.2.1.1 255.255.255.240
> > > > !
> > > > router bgp 1
> > > > bgp log-neighbor-changes
> > > > network 170.2.1.0 mask 255.255.255.240
> > > > neighbor 192.168.2.2 remote-as 2
> > > > neighbor 192.168.2.2 route-map BGP_MAP out
> > > > neighbor 192.168.2.3 remote-as 2
> > > > no auto-summary
> > > > !
> > > > route-map BGP_MAP permit 10
> > > > set metric 20
> > > >
> > > > *********************************************
> > > > R1#sh ip bgp
> > > > BGP table version is 8, local router ID is
> > > > 172.10.1.1
> > > > 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
> > > > *> 170.2.1.0/28 192.168.2.1 0
> > > > 100 0 1 i
> > > > * i 192.168.1.2 20
> > > > 100 0 1 i
> > > > *********************************************
> > > > R2#sh ip bgp
> > > > BGP table version is 8, local router ID is
> > > > 192.168.2.2
> > > > 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
> > > > * i170.2.1.0/28 192.168.1.1 0
> > > > 100 0 1 i
> > > > *> 192.168.2.1 20
> > > > 100 0 1 i
> > > > *********************************************
> > > >
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