From: Narvaez, Pablo (Pablo.Narvaez@xxxxxxxxxxxxx)
Date: Sat Apr 06 2002 - 19:55:11 GMT-3
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 t
his: (?)
- 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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