From: Simon Baxter (Simon.Baxter@xxxxxxxxxxxxxx)
Date: Thu Aug 10 2000 - 02:16:54 GMT-3
Well done Aaron!!
Simple and obvious mistake (now that you explained it so clearly!!)
I hope I'm as confident on the day!!
-----Original Message-----
From: Aaron K. Dixon [mailto:adixon@smc.omnes.slb.com]
Sent: Thursday, August 10, 2000 3:15 PM
To: Kenny Sallee; Scott; ccielab@groupstudy.com
Subject: RE: BGP routing loop?
I just set this up in the lab and confirmed that the problem is a recursive
look-up issue with the route for the loopback being learned via RIP and then
BGP.
Notice the route for the 4.4.4.4 address:
r7#s ip bgp 4.4.4.4
BGP routing table entry for 4.4.4.0/24, version 3
Paths: (1 available, best #1)
4
4.4.4.4 (metric 11) from 4.4.4.4 (215.6.11.1)
Origin IGP, metric 0, localpref 100, valid, external, best
4.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
B 4.4.4.0/24 [20/0] via 4.4.4.4, 00:00:06
R 4.0.0.0/8 [120/11] via 172.16.24.4, 00:00:05, Serial0
172.16.0.0/24 is subnetted, 2 subnets
C 172.16.24.0 is directly connected, Serial0
C 172.16.2.0 is directly connected, Loopback0
The route is learned with a next hop of the same address. This route now
replaces the RIP route.
r7#s ip bgp 4.4.4.4
BGP routing table entry for 4.4.4.0/24, version 26
Paths: (1 available, no best path)
4
4.4.4.4 (inaccessible) from 4.4.4.4 (215.6.11.1)<====Notice that this
route is now inaccessible
Origin IGP, metric 0, localpref 100, valid, external
R 4.0.0.0/8 [120/11] via 172.16.24.4, 00:00:27, Serial0
172.16.0.0/24 is subnetted, 2 subnets
C 172.16.24.0 is directly connected, Serial0
C 172.16.2.0 is directly connected, Loopback0
Once the route shows up as inaccessible in the BGP table all BGP routes are
dropped. Once this happens the RIP route takes over again and the BGP
routes are re-learned. This process cycles about every 60 seconds on
average.
The solution is to ensure that there is always a non-BGP route to the eBGP
multi-hop neighbor address.
Regards,
Aaron K. Dixon
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Kenny Sallee
Sent: Wednesday, August 09, 2000 11:28 PM
To: Scott; ccielab@groupstudy.com
Subject: Re: BGP routing loop?
I would look at RIP. Since connectivity to the loopbacks is provided by
RIP, if RIP is hosed somehow ( RIP routes being removed from the route
table ) then BGP will break. Try a "debug ip rip events" and send the
output to the list. I'd also remove the "network 4.4.4.0" statement from
BGP on the second router, not sure why but it may cause you problems. Also,
there's an offset list applied to RIP adding 10 hops for some reason....Why?
Just curious...
Kenny
----- Original Message -----
From: "Scott" <trig@usa.net>
To: <ccielab@groupstudy.com>
Sent: Wednesday, August 09, 2000 7:49 PM
Subject: BGP routing loop?
> Hello
>
> I was trying to connect two AS with a EBGP multihop command between two
> loopbacks and it looks like I am getting a some type of routing loop. The
BGP
> routes are put in the routing table and removed every 60 seconds (see
> attached). I have IP connectivity via RIP and the connection is showing
as
> established. Any suggestions? Thanks
>
> Scotty
>
>
> router2#show ip route
> Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
> D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
> N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
> E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
> i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate
> default
> U - per-user static route, o - ODR
>
> Gateway of last resort is not set
>
> 138.6.0.0/24 is subnetted, 2 subnets
> B 138.6.5.0 [200/0] via 172.16.35.5, 00:09:52
> B 138.6.1.0 [200/0] via 172.16.35.5, 00:09:52
> 4.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
> B 4.4.4.0/24 [20/0] via 4.4.4.4, 00:00:36
> R 4.0.0.0/8 [120/11] via 172.16.24.4, 00:00:27, Serial1
> 172.16.0.0/24 is subnetted, 5 subnets
> O IA 172.16.35.0 [110/74] via 172.16.23.3, 00:10:44, Ethernet0
> C 172.16.24.0 is directly connected, Serial1
> C 172.16.23.0 is directly connected, Ethernet0
> C 172.16.12.0 is directly connected, Serial0
> C 172.16.2.0 is directly connected, Loopback0
> router2#ping 4.4.4.4
>
> Type escape sequence to abort.
> Sending 5, 100-byte ICMP Echos to 4.4.4.4, timeout is 2 seconds:
> .....
> Success rate is 0 percent (0/5)
> router2#
> 05:08:12: BGP: no valid path for 4.4.4.0/24
> 05:08:12: BGP: nettable_walker 4.4.4.0/24 no best path
> 05:08:12: BGP: 4.4.4.4 computing updates, neighbor version 15, table
version
> 16,
> starting at 0.0.0.0
> 05:08:12: BGP: 4.4.4.4 update run completed, ran for 0ms, neighbor version
15,
> s
> tart version 16, throttled to 16, check point net 0.0.0.0
> 05:08:12: BGP: 172.16.23.1 computing updates, neighbor version 15, table
> version
> 16, starting at 0.0.0.0
> 05:08:12: BGP: 172.16.23.1 send UPDATE 4.4.4.0/24 -- unreachable
> 05:08:12: BGP: 172.16.23.1 1 updates enqueued (average=27, maximum=27)
> 05:08:12: BGP: 172.16.23.1 update run completed, ran for 8ms, neighbor
version
> 1
> 5, start version 16, throttled to 16, check point net 0.0.0.0
> 05:08:12: BGP: 172.16.23.3 computing updates, neighbor version 15, table
> version
>
> !
> interface Loopback0
> ip address 172.16.2.2 255.255.255.0
> no ip directed-broadcast
> !
> !
> interface Serial1
> ip address 172.16.24.2 255.255.255.0
> no ip directed-broadcast
> clockrate 64000
> !
> interface BRI0
> no ip address
> no ip directed-broadcast
> shutdown
> !
> router ospf 3
> network 172.16.23.0 0.0.0.255 area 3
> !
> router rip
> version 2
> network 172.16.0.0
> default-information originate
> !
> router bgp 3
> no synchronization
> network 172.16.2.0 mask 255.255.255.0
> neighbor 4.4.4.4 remote-as 4
> neighbor 4.4.4.4 ebgp-multihop 5
> neighbor 4.4.4.4 update-source Loopback0
> neighbor 4.4.4.4 distribute-list 2 out
> neighbor 172.16.23.1 remote-as 3
> neighbor 172.16.23.3 remote-as 3
> !
>
>
> Router 1
> !
> interface Loopback0
> ip address 4.4.4.4 255.255.255.0
> no ip directed-broadcast
> !
> interface Loopback1
> ip address 215.6.10.1 255.255.255.0
> no ip directed-broadcast
> !
> interface Loopback2
> ip address 215.6.11.1 255.255.255.0
> no ip directed-broadcast
> !
> interface Loopback5
> no ip address
> no ip directed-broadcast
> !
> interface Ethernet0
> no ip address
> no ip directed-broadcast
> appletalk cable-range 600-600 600.5
> appletalk zone biteme
> appletalk protocol eigrp
> bridge-group 1
> !
> interface Serial0
> ip address 172.16.24.4 255.255.255.0
> no ip directed-broadcast
> no ip mroute-cache
> no fair-queue
> !
> interface Serial1
> ip address 172.16.10.10 255.255.255.252
> no ip directed-broadcast
> bridge-group 1
> !
> interface BRI0
> no ip address
> no ip directed-broadcast
> shutdown
> !
> router rip
> version 2
> offset-list 1 out 10
> network 4.0.0.0
> network 172.16.0.0
> !
> router bgp 4
> no synchronization
> network 4.4.4.0 mask 255.255.255.0
> neighbor 172.16.2.2 remote-as 3
> neighbor 172.16.2.2 ebgp-multihop 5
> neighbor 172.16.2.2 update-source Loopback0
>
>
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