From: Brian Edwards (bedwards@xxxxxxxxxxx)
Date: Thu Aug 10 2000 - 02:18:55 GMT-3
This is great. Kieth you are just about right on, but the problem isn't
Admin Distance, it is prfix length. The RIP route is 4.0.0.0/8 (RIP version
2 is still classful). This route is used to set up the eBGP session. Then
the route 4.4.4.0/24 route is learned via BGP with a next hop 4.4.4.4.
The easiest way to fix it is to remove the network 4.4.4.0... statment out
of BGP. Do you absolutely have to have this in there? If so there are some
interesting ways to get this to work.
> -----Original Message-----
> From: Keith Kruepke [mailto:lister@kruepke.com]
> Sent: Wednesday, August 09, 2000 9:16 PM
> To: Scott; ccielab@groupstudy.com
> Subject: Re: BGP routing loop?
>
>
> Scott,
>
> I think this line from your routing table may be part of the problem:
>
> B 4.4.4.0/24 [20/0] via 4.4.4.4, 00:00:36
>
> The route to 4.4.4.0/24 goes through 4.4.4.4--that doesn't
> seem right to me.
>
> I'm guessing that 4.4.4.0 is initially learned via RIP, so
> that you can get to 4.4.4.4 and start an EBGP session. Then
> the EBGP neighbor advertises 4.4.4.0 to router2, and that
> route would take precedence in the IP routing table (AD of 20
> is much better than RIP). Then the RIP route is gone, so
> connectivity is lost, and the EBGP route disappears. Then
> the RIP route returns, and connectivity is reestablished, and
> the cycle continues.
>
> Based on the description, this is my theory, but maybe
> someone has another idea? I think this is part of the reason
> you would normally want to use the directly connected
> interface IPs as the neighbor addresses for EBGP under most
> circumstances. If you still want to use the loopbacks, I
> would put in static routes to those networks, rather than using RIP.
>
> Keith
>
> ----- Original Message -----
> From: "Scott" <trig@usa.net>
> To: <ccielab@groupstudy.com>
> Sent: Wednesday, August 09, 2000 9:49 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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