Nate,
this works perfectly fine for me.
R1 <> R2 <> R3 <> R4
R1-4 are in AS 1
R2-3 in AS 23
1.1.1.1 and 4.4.4.4 are Lo0 IP addressess off R1 and R4 respectively.
All routers run the same IOS on 7200 platform (Dynamips)
R4#sh ver | in IOS
Cisco IOS Software, 7200 Software (C7200-K91P-M), Version 12.2(25)S13,
RELEASE SOFTWARE (fc1)
====
R1#sh run | b bgp
router bgp 1
bgp router-id 1.1.1.1
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor 12.12.12.2 remote-as 23
!
address-family ipv4
neighbor 12.12.12.2 activate
neighbor 12.12.12.2 allowas-in
no auto-summary
no synchronization
network 1.1.1.1 mask 255.255.255.255
exit-address-family
R1#sh ip bgp | b Net
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 0.0.0.0 0 32768 i
*> 4.4.4.4/32 12.12.12.2 0 23 1 i
===
R2#sh run | b bgp
router bgp 23
bgp router-id 2.2.2.2
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor 3.3.3.3 remote-as 23
neighbor 3.3.3.3 update-source Loopback0
neighbor 12.12.12.1 remote-as 1
!
address-family ipv4
neighbor 3.3.3.3 activate
neighbor 3.3.3.3 next-hop-self
neighbor 12.12.12.1 activate
no auto-summary
no synchronization
exit-address-family
===
R3#sh run | beg bgp
router bgp 23
bgp router-id 3.3.3.3
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor 2.2.2.2 remote-as 23
neighbor 2.2.2.2 update-source Loopback0
neighbor 34.34.34.4 remote-as 1
!
address-family ipv4
neighbor 2.2.2.2 activate
neighbor 2.2.2.2 next-hop-self
neighbor 34.34.34.4 activate
no auto-summary
no synchronization
exit-address-family
===
router bgp 1
bgp router-id 4.4.4.4
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor 34.34.34.3 remote-as 23
!
address-family ipv4
neighbor 34.34.34.3 activate
neighbor 34.34.34.3 allowas-in
no auto-summary
no synchronization
network 4.4.4.4 mask 255.255.255.255
exit-address-family
R4#sh ip bgp | b Net
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 34.34.34.3 0 23 1 i
*> 4.4.4.4/32 0.0.0.0 0 32768 i
===
HTH
A.
2009/10/21 Nate Lee <natetlee_at_gmail.com>
> Thanks everybody, I do have the allowas-in command configured on the
> routers
> residing in AS 100 on both sides, from what the show ip bgp neighbor
> x.x.x.x
> advertised-routes is telling me though, the eBGP peer that resides in AS
> 200
> is not even trying to send the route from the other side of my
> discontiguous
> AS 100. It will send any routes that originate in AS 200, but not from the
> other AS 100.
>
> As a quick snapshot, it is setup as such:
>
> R4 <> R2 <> R1 <> R3 <> R5
>
> With R4 and R5 being in AS 100 and R1, R2 and R3 fully meshed iBGP peers in
> AS 200.
>
> The 4.0.0.0 is being originated from R4 and 5.0.0.0 is being originated
> from
> R5, both routes make it to all routers in AS 200 but neither makes it to
> the
> far side AS 100 router.
>
> From R2:
>
> R2(config)#*do sho ip bgp*
> BGP table version is 4, local router ID is 2.2.2.2
> Status codes: s suppressed, d damped, h history, * valid, > best, i -
> internal,
> r RIB-failure, S Stale
> Origin codes: i - IGP, e - EGP, ? - incomplete
>
> Network Next Hop Metric LocPrf Weight Path
> *> 4.0.0.0 10.1.24.4 0 0 100 i
> * i5.0.0.0 10.1.35.5 0 100 0 100 i
>
> R2(config)#*do sho ip bgp neigh 10.1.24.4 advertised-routes*
>
> Total number of prefixes 0
>
> R2(config)#*do sh run | s bgp 200*
> router bgp 200
> no synchronization
> bgp log-neighbor-changes
> neighbor 10.1.24.4 remote-as 100
> neighbor 10.1.123.1 remote-as 200
> neighbor 10.1.123.3 remote-as 200
> no auto-summary
> R2(config)#
>
> R4#*sh run | s bgp 100*
> router bgp 100
> no synchronization
> bgp log-neighbor-changes
> network 4.0.0.0
> neighbor 10.1.24.2 remote-as 200
> neighbor 10.1.24.2 allowas-in
> no auto-summary
>
> And on R4, you can see it never received any prefixes:
>
> R4#*show ip bgp neighbors 10.1.24.2 | in Prefixes|Sent*
> Sent Rcvd
> Sent Rcvd
> Prefixes Current: 1 0
> Prefixes Total: 1 0
>
> There is no filtering going on throughout the topology, the only
> non-standard thing is the discontiguous AS.
>
>
> On Tue, Oct 20, 2009 at 8:24 AM, Victor Cappuccio <vcappuccio_at_gmail.com
> >wrote:
>
> > Hi,
> >
> > Like Andrew said you can use allowas-in to prevent this from happening:
> > to prevent this happening: *Mar 1 00:05:34.851: BGP(0): 10.1.12.2 rcv
> > UPDATE about 3.3.3.3/32 -- DENIED due to: AS-PATH contains our own AS;
> > the thing here is that the other routers will have back the route from
> the
> > next hop AS, now if allowed to use VRF to solve this issue, using the
> > as-overrride feature
> > http://anetworkerblog.com/2008/05/11/neighbor-ce-as-override/
> > making Narbik Happy by using a 007 stuff here :-)
> >
> >
> > R2(config-router)#do show run | b router bgp
> > router bgp 200
> > bgp log-neighbor-changes
> > !
> > address-family ipv4
> > no auto-summary
> > no synchronization
> > exit-address-family
> > !
> > address-family ipv4 vrf X
> > neighbor 10.1.12.1 remote-as 100
> > neighbor 10.1.12.1 activate
> > neighbor 10.1.12.1 as-override
> > neighbor 10.1.23.3 remote-as 100
> > neighbor 10.1.23.3 activate
> > neighbor 10.1.23.3 as-override
> > no synchronization
> > exit-address-family
> > !
> > R2(config-router)#do show ip bgp vpnv4 all
> > BGP table version is 7, local router ID is 10.1.23.2
> > Status codes: s suppressed, d damped, h history, * valid, > best, i -
> > internal,
> > r RIB-failure, S Stale
> > Origin codes: i - IGP, e - EGP, ? - incomplete
> > Network Next Hop Metric LocPrf Weight Path
> > Route Distinguisher: 1:1 (default for vrf X)
> > *> 1.1.1.1/32 10.1.12.1 0 0 100 i
> > *> 3.3.3.3/32 10.1.23.3 0 0 100 i
> > R2(config-router)#do show ip bgp vpnv4 all neigh 10.1.23.3 ad
> > BGP table version is 7, local router ID is 10.1.23.2
> > Status codes: s suppressed, d damped, h history, * valid, > best, i -
> > internal,
> > r RIB-failure, S Stale
> > Origin codes: i - IGP, e - EGP, ? - incomplete
> > Network Next Hop Metric LocPrf Weight Path
> > Route Distinguisher: 1:1 (default for vrf X)
> > *> 1.1.1.1/32 10.1.12.1 0 0 100 i
> > Total number of prefixes 1
> > R2(config-router)#do show ip bgp vpnv4 all neigh 10.1.12.1 ad
> > BGP table version is 7, local router ID is 10.1.23.2
> > Status codes: s suppressed, d damped, h history, * valid, > best, i -
> > internal,
> > r RIB-failure, S Stale
> > Origin codes: i - IGP, e - EGP, ? - incomplete
> > Network Next Hop Metric LocPrf Weight Path
> > Route Distinguisher: 1:1 (default for vrf X)
> > *> 3.3.3.3/32 10.1.23.3 0 0 100 i
> > Total number of prefixes 1
> > and
> > R3#show ip bgp
> > BGP table version is 5, local router ID is 10.1.12.1
> > Status codes: s suppressed, d damped, h history, * valid, > best, i -
> > internal,
> > r RIB-failure, S Stale
> > Origin codes: i - IGP, e - EGP, ? - incomplete
> > Network Next Hop Metric LocPrf Weight Path
> > *> 1.1.1.1/32 10.1.23.2 0 200 200 i
> > *> 3.3.3.3/32 0.0.0.0 0 32768 i
> >
> > Just my 2 cents!
> > Victor.-
> >
> >
> >
> >
> > On Tue, Oct 20, 2009 at 6:35 AM, ALL From_NJ <all.from.nj_at_gmail.com
> >wrote:
> >
> >> I would re-check your setup.
> >>
> >> You are right, the allow-as will simply allow in the local AS x number
> of
> >> times in the path. This is done on the receiving end.
> >>
> >> If you changed your set up some, and one side has the AS 101, is the
> >> problem
> >> present? I might suggest to try this and make sure all BGP is cool
> first.
> >>
> >> Also, you can prepend an AS on advertisement, so you can leave the one
> >> side
> >> with AS 101 as is and simply send out a route with AS 100 in the path.
> >> The
> >> AS 100 router should not accept it. This is another way to test the
> >> allowed-as command.
> >>
> >> Create a new loopback on AS 101 and prepend AS 100 in it.
> >>
> >> HTH,
> >>
> >> Andrew Lee Lissitz
> >>
> >>
> >>
> >>
> >>
> >> On Mon, Oct 19, 2009 at 11:12 PM, Nate Lee <natetlee_at_gmail.com> wrote:
> >>
> >> > I have a scenario labbed up where I have an discontiguous BGP AS split
> >> by
> >> > another AS, something like this: (AS100) <> (AS 200) <> (AS 100).
> >> >
> >> > I am trying to get the prefixes on the AS 100 routers to show up in
> each
> >> > others BGP tables. I have implemented the neighbor x.x.x.x allowas-in
> >> > command on the AS 100 routers on their neighbor statements facing the
> AS
> >> > 200
> >> > routers but it does not seem to work. When I do a SHOW IP BGP NEIGH
> >> > x.x.x.x
> >> > ADVERTISED-ROUTES on the AS 200 routers, I see that the AS 200 router
> >> will
> >> > not send the route that originated in the far side AS 100.
> >> >
> >> > Is there some sort of configuration needed on the AS 200 routers to
> >> allow
> >> > them to send a route with an AS PATH that contains the AS they are
> >> sending
> >> > into? I was under the impression that they do not perform an outgoing
> >> AS
> >> > PATH check.
> >> >
> >> > Thanks!
> >> >
> >> > Nate
> >> >
> >> >
> >> > Blogs and organic groups at http://www.ccie.net
> >> >
> >> >
> _______________________________________________________________________
> >> > Subscription information may be found at:
> >> > http://www.groupstudy.com/list/CCIELab.html
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >
> >>
> >>
> >> --
> >> Andrew Lee Lissitz
> >> all.from.nj_at_gmail.com
> >>
> >>
> >> Blogs and organic groups at http://www.ccie.net
> >>
> >> _______________________________________________________________________
> >> Subscription information may be found at:
> >> http://www.groupstudy.com/list/CCIELab.html
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >
> >
> > --
> > Victor Cappuccio
> > CCIE R/S# 20657
> > CCSI# 30452
> > www.anetworkerblog.com
> > www.linkedin.com/in/vcappuccio
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
Blogs and organic groups at http://www.ccie.net
Received on Wed Oct 21 2009 - 13:51:21 ART
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