From: Narvaez, Pablo (Pablo.Narvaez@xxxxxxxxxxxxx)
Date: Sat Apr 06 2002 - 20:27:47 GMT-3
ummm I think your route is damnt hehe .... sorry about that. ummmm if you check
the attribs between them you'll see that
r3 is choosing "theorically" the worst route. Weight is the same, Local-Pref is
better thru 26.1.1.2, asp-path is shorter thru 26.1.1.2 and also med is lower
.... can you do a "show ip bgp 192.168.1.0" ... at the first sight I wonder why
that route is going thru 10.1.1.1 instead of 26.1.1.2.
The only thing that comes to my head is the next hop is not available or if tha
t route is internal, you have sync enabled and that route is not known thru IG
P.
hockito :o
-----Original Message-----
From: ying chang [mailto:ying_c@hotmail.com]
Sent: Sabado, 06 de Abril de 2002 05:17 p.m.
To: Narvaez, Pablo; Upp_and_Upp@hotmail.com; ccielab@groupstudy.com
Subject: RE: BGP MED - again
Hi hockito,
Sorry, you are right. Can you explain why I get the following (192.168.1.0)
which is the route from R1:
r3#sib
BGP table version is 5, local router ID is 36.1.1.3
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
*>i26.1.1.0/24 36.1.1.6 0 100 0 i
*> 36.1.1.0/24 0.0.0.0 0 32768 i
* i 36.1.1.6 0 100 0 i
* i192.168.1.0 26.1.1.2 20 100 0 1 i
*> 10.1.1.1 30 0 1 1 1 i
r3#
Thanks,
Chang
>From: "Narvaez, Pablo" <Pablo.Narvaez@getronics.com>
>Reply-To: "Narvaez, Pablo" <Pablo.Narvaez@getronics.com>
>To: "ying chang" <ying_c@hotmail.com>, <Upp_and_Upp@hotmail.com>,
><ccielab@groupstudy.com>
>Subject: RE: BGP MED - again
>Date: Sat, 6 Apr 2002 16:55:11 -0600
>
>ummm isn't as-path compared first that ibgp vs ebgp ?
>
>I'll ommit some attribs checked in between for path selection, but isn't
>like this: (?)
>
>- weight
>- local-pref
>- as-path
>- med
>- ebgp vs ibgp
>
>??
>
>So that would give us as-path comparision before ebgp-igrp, correct?
>
>If you prepend from r2 to r3 thru r6, I think r3 will send that route
>prepended, which cause that r1 selects that route thru r2. This way you'll
>have touched only r2 and r1 will see r1-r2.
>
>Am I right?
>
>hockito
>
>
>
>
>-----Original Message-----
>From: ying chang [mailto:ying_c@hotmail.com]
>Sent: Sabado, 06 de Abril de 2002 04:29 p.m.
>To: Upp_and_Upp@hotmail.com; ccielab@groupstudy.com
>Subject: Re: BGP MED - again
>
>
>Hi Sean,
>
>Thanks. Please check R3's BGP table. My topology is
>
> -----R1(AS1)-----
> | |
> R2 R3
> |----R6---------| (R2, R3, R6 are in AS236)
>
>As you can see MED is comparision is skipped. as-path will not do anything
>for this case, because ebgp route is preferred as we've seen from Peter's
>example - as-path comparision come after ebgp-ibgp comparision.
>
>Thanks,
>Chang
>
>R1: AS1 (ISP router)
>
>interface Loopback0
>ip address 192.168.1.1 255.255.255.0
>!
>interface Ethernet0
>no ip address
>shutdown
>!
>interface Serial0
>ip address 10.1.1.1 255.255.255.0
>encapsulation frame-relay
>no fair-queue
>frame-relay map ip 10.1.1.2 110 broadcast
>frame-relay map ip 10.1.1.3 120 broadcast
>no frame-relay inverse-arp
>!
>router bgp 1
>bgp log-neighbor-changes
>network 192.168.1.0
>neighbor 10.1.1.2 remote-as 236
>neighbor 10.1.1.2 soft-reconfiguration inbound
>neighbor 10.1.1.2 route-map set-med1 out
>neighbor 10.1.1.3 remote-as 236
>neighbor 10.1.1.3 soft-reconfiguration inbound
>neighbor 10.1.1.3 route-map set-med2 out
>!
>!
>route-map set-med2 permit 10
>set metric 30
>set as-path prepend 1 1
>!
>route-map set-med1 permit 10
>set metric 20
>!
>
>R2: (AS236, border router 1 to R1)
>!
>interface Ethernet1
>ip address 26.1.1.2 255.255.255.0
>!
>interface Serial0
>ip address 10.1.1.2 255.255.255.0
>encapsulation frame-relay
>no fair-queue
>frame-relay map ip 10.1.1.1 111 broadcast
>frame-relay map ip 10.1.1.3 111 broadcast
>!
>router ospf 100
>router-id 26.1.1.2
>log-adjacency-changes
>passive-interface default
>no passive-interface Ethernet1
>no passive-interface Serial0
>network 0.0.0.0 255.255.255.255 area 0
>!
>router bgp 236
>bgp router-id 26.1.1.2
>bgp always-compare-med
>bgp log-neighbor-changes
>neighbor 10.1.1.1 remote-as 1
>neighbor 10.1.1.1 soft-reconfiguration inbound
>neighbor 26.1.1.6 remote-as 236
>neighbor 26.1.1.6 next-hop-self
>neighbor 36.1.1.3 remote-as 236
>neighbor 36.1.1.3 next-hop-self
>neighbor 36.1.1.3 soft-reconfiguration inbound
>!
>
>R3: (AS236, border router 2 to R1)
>
>!
>interface Ethernet0
>ip address 36.1.1.3 255.255.255.0
>!
>interface Serial0
>ip address 10.1.1.3 255.255.255.0
>encapsulation frame-relay
>no fair-queue
>frame-relay map ip 10.1.1.1 121 broadcast
>frame-relay map ip 10.1.1.2 121 broadcast
>!
>!
>router ospf 100
>router-id 36.1.1.3
>log-adjacency-changes
>passive-interface default
>no passive-interface Ethernet0
>no passive-interface Serial0
>network 0.0.0.0 255.255.255.255 area 0
>!
>router bgp 236
>bgp always-compare-med
>bgp log-neighbor-changes
>bgp always-compare-med
>network 36.1.1.0 mask 255.255.255.0
>neighbor 10.1.1.1 remote-as 1
>neighbor 10.1.1.1 soft-reconfiguration inbound
>neighbor 26.1.1.2 remote-as 236
>neighbor 26.1.1.2 next-hop-self
>neighbor 26.1.1.2 soft-reconfiguration inbound
>neighbor 36.1.1.6 remote-as 236
>neighbor 36.1.1.6 next-hop-self
>neighbor 36.1.1.6 soft-reconfiguration inbound
>!
>
>(R6: internal router, IBGP to R2 and R3 only)
>!
>interface Ethernet0
>ip address 26.1.1.6 255.255.255.0
>!
>interface Ethernet1
>ip address 36.1.1.6 255.255.255.0
>!
>!
>router ospf 100
>router-id 36.1.1.6
>log-adjacency-changes
>passive-interface default
>no passive-interface Ethernet0
>no passive-interface Ethernet1
>network 0.0.0.0 255.255.255.255 area 0
>!
>router bgp 236
>no synchronization
>bgp router-id 36.1.1.6
>bgp always-compare-med
>bgp log-neighbor-changes
>bgp deterministic-med
>network 26.1.1.0 mask 255.255.255.0
>network 36.1.1.0 mask 255.255.255.0
>neighbor 26.1.1.2 remote-as 236
>neighbor 26.1.1.2 soft-reconfiguration inbound
>neighbor 36.1.1.3 remote-as 236
>neighbor 36.1.1.3 soft-reconfiguration inbound
>!
>-------------------------------------------------------
>BGP tables
>-------------------------------------------------------
>r1#sib
>BGP table version is 25, local router ID is 192.168.1.1
>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
>* 26.1.1.0/24 10.1.1.2 0 236 i
>*> 10.1.1.3 0 236 i
>* 36.1.1.0/24 10.1.1.2 0 236 i
>*> 10.1.1.3 0 0 236 i
>*> 192.168.1.0 0.0.0.0 0 32768 i
>r1#
>termserv#2
>[Resuming connection 2 to r2 ... ]
>
>r2#sib
>BGP table version is 4, local router ID is 26.1.1.2
>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
>*>i26.1.1.0/24 26.1.1.6 0 100 0 i
>*>i36.1.1.0/24 26.1.1.6 0 100 0 i
>* i 36.1.1.3 0 100 0 i
>*> 192.168.1.0 10.1.1.1 20 0 1 i
>* i 36.1.1.3 30 100 0 1 1 1 i
>r2#
>termserv#3
>[Resuming connection 3 to r3 ... ]
>
>r3#sib
>BGP table version is 5, local router ID is 36.1.1.3
>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
>*>i26.1.1.0/24 36.1.1.6 0 100 0 i
>*> 36.1.1.0/24 0.0.0.0 0 32768 i
>* i 36.1.1.6 0 100 0 i
>* i192.168.1.0 26.1.1.2 20 100 0 1 i
>*> 10.1.1.1 30 0 1 1 1 i
>r3#
>termserv#6
>[Resuming connection 6 to r6 ... ]
>
>r6#sib
>BGP table version is 8, local router ID is 36.1.1.6
>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
>*> 26.1.1.0/24 0.0.0.0 0 32768 i
>*> 36.1.1.0/24 0.0.0.0 0 32768 i
>* i 36.1.1.3 0 100 0 i
>*>i192.168.1.0 26.1.1.2 20 100 0 1 i
>* i 36.1.1.3 30 100 0 1 1 1 i
>r6#
>
>
>
> >From: "Sean C." <Upp_and_Upp@hotmail.com>
> >Reply-To: "Sean C." <Upp_and_Upp@hotmail.com>
> >To: "ying chang" <ying_c@hotmail.com>, <ccielab@groupstudy.com>
> >Subject: Re: BGP MED - again
> >Date: Sat, 6 Apr 2002 16:50:54 -0800
> >
> >Hi Chang,
> >
> >Concerning your question of how to manipulate routes so the routes will
>be
> >preferred on the R1-R3 link over R2-R3 routes while not being able to
> >change
> >the configs on R1 and R3 (in other words - you can only work on R3) - add
>a
> >route-map on R3 and prepend R3's own AS# to routes being advertised to
>R2.
> >Since shorter AS paths are preferred, the routes will all come in on the
> >R1-R3 route which has a shorter AS path. Plus, you don't have to
> >manipulate anything on R2 and R1.
> >
> >Hope this helps,
> >Sean
> >----- Original Message -----
> >From: "ying chang" <ying_c@hotmail.com>
> >To: <dan_schaw@yahoo.com>; <jgraun@attbi.com>; <pdostal@724.com>;
> ><ccielab@groupstudy.com>
> >Sent: Saturday, April 06, 2002 12:47 PM
> >Subject: RE: BGP MED - again
> >
> >
> >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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