From: ying chang (ying_c@xxxxxxxxxxx)
Date: Sat Apr 06 2002 - 21:30:17 GMT-3
Hi Sean,
Here's the trace. The prepend is applied at R1-R3 route from R1, which I'm
hoping to make R3 sees it as less actractive route:
r3#sib
BGP table version is 9, 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#trace 26.1.1.2
Type escape sequence to abort.
Tracing the route to 26.1.1.2
1 36.1.1.6 4 msec 4 msec 4 msec
2 26.1.1.2 8 msec * 4 msec
r3#trace 10.1.1.2
Type escape sequence to abort.
Tracing the route to 10.1.1.2
1 10.1.1.1 20 msec 20 msec 20 msec
2 10.1.1.2 40 msec * 32 msec
r3#
Thanks,
Chang
>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 19:03:23 -0800
>
>Hi Chang,
>
>OK, clouds are clearing. Knock that sync off on AS 236. R3 wants to be
>synced with R2 but isn't. See what happens then.
>Also, when you're pinging 26.1.1.2, trace it - I'm wondering if you're
>going thru R1.
>Sean
>
>
>----- Original Message -----
>From: "ying chang" <ying_c@hotmail.com>
>To: <Upp_and_Upp@hotmail.com>
>Sent: Saturday, April 06, 2002 3:53 PM
>Subject: Re: BGP MED - again
>
>
>Hi Sean,
>
>Thanks for the help and sorry about the confusion. R3 learned 192.168.1.0
>from ebgp peer R1 and ibgp peer R2. I'm trying to ask R3 instead of using
>its direct connected route to AS1 (R1), use R3->R2->R1 route. The only
>router we are allowed to change is R1. R2, R3, R6 has fully meshed ibgp and
>ospf running among themselves.
>
>It's originated from Peter's post, I just trying explore it a little more.
>
>Thanks,
>Chang
>
>
> >From: "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 18:28:23 -0800
> >
> >Hi Chang,
> >
> >What are you looking for from 192.168.1.0? Why the route appears twice
>in
> >R3's BGP table, or why R3 picks the route from 10.1.1.1(R1) over
> >26.1.1.2(R2).
> >
> >If you want to know why R3 picks the 192.168.1.0 route from R1 instead of
> >going around R2 to R1, it's because the path to R1 only has 1 AS#, R2's
>path
> >has AS#1 prepended twice.
> >
> >Is this what you are looking for? Sorry, I'm trying to help but I'm
>trying
> >to understand what exactly you are looking for.
> >Sean
> >----- Original Message -----
> >From: "ying chang" <ying_c@hotmail.com>
> >To: <Pablo.Narvaez@getronics.com>; <Upp_and_Upp@hotmail.com>;
> ><ccielab@groupstudy.com>
> >Sent: Saturday, April 06, 2002 3:16 PM
> >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
> > > > > > *********************************************
> > > > > >
This archive was generated by hypermail 2.1.4 : Thu Jun 13 2002 - 10:57:58 GMT-3