From: Roger Schotsal (schotsal@xxxxxxxxxxx)
Date: Mon Jun 17 2002 - 16:33:48 GMT-3
I took a few minuets to think about your senario. I think it behaves as it
should.
BGP will not place a route in the table unless the route is in the in the
IGP - if the route is learned from an iBGP neighbor. Routers B & D learn
the routers from eBGP neighbors (different confederation ASs). Router B (AS
65531) learns the route from router A (65530) - this is an eBGP like session
- the route is placed in the routing table & is thus advertised to its
neighbors. This same method works to propegate the route to router D.
Router B also advertises the route to router C - but since thay are in the
same AS - router C does not place the route in the routing table without a
IGP route to support it.
As you discovered - this can be fixed by disableing synchronization on
router C & E.
Note - in you config - I did not see an ospf route for 150.150.150.0/24 - I
am assuming you did not add that route to ospf.
thanx,
Roger
>From: Hunt Lee <ciscoforme3@yahoo.com.au>
>Reply-To: Hunt Lee <ciscoforme3@yahoo.com.au>
>To: ccielab@groupstudy.com
>Subject: BGP w/ no synchronization
>Date: Sun, 16 Jun 2002 21:05:07 +1000 (EST)
>
>Okay folks, starting off some late nite studying and just noticed something
>weird. Got a Confederation setup like:
>
>150.150.150.0/24---RTA ---RTB ---RTD---RTF
> | |
> RTC RTE
>
>RTA, B, C, D, & E are in a Confederation called AS 1, in which:-
>
>RTA is sub-AS 65530
>RTB & RTC are both in sub-AS 65531
>RTD & RTE are both in sub-AS 65532
>
>RTF is in AS 2
>
>RTB, C, D & E are running OSPF as IGP. And OSPF is being redistributed
>into
>BGP at RTB.
>
>The network 150.150.150.0/24 is being advertised into BGP by BGP "network"
>command on RTA.
>
>Ok, here is the thing. The 150.150.150.0/24 network is being seen by RTA,
>RTB,
>RTD, & RTF. I could ping 150.150.150.1 from these four routers. However,
>it
>can't be seen by RTC & RTE (shown as follows). But when I put "no
>synchronization" on the middle four routers (RTB, RTC, RTD, & RTE), then
>everything becomes fine again... I thought since I used IGP (OSPF), and
>if
>the router can see the EBGP Next-Hop (193.16.0.2) in their routing table,
>then
>the synch. rule shouldn't apply anymore.
>
>Am I missing something here?
>
>RouterC#sh ip bgp
>BGP table version is 4, local router ID is 172.16.0.2
>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
>* i150.150.150.0/24 193.16.0.2 0 100 0 (65530) i
><-----193.16.0.2 is the Serial int of RTA
>
>*>i172.16.0.0/30 172.16.0.1 0 100 0 ?
>* i172.16.0.12/30 172.16.0.18 30 100 0 ?
>*>i172.16.0.16/30 172.16.0.1 0 100 0 ?
>*>i193.16.0.0/30 172.16.0.1 0 100 0 ?
>* i193.16.0.8/30 172.16.0.18 0 100 0 (65532) i
>RouterC#sh 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
>
> 172.16.0.0/30 is subnetted, 3 subnets
>O 172.16.0.16 [110/128] via 172.16.0.1, 01:35:04, Serial1
>O 172.16.0.12 [110/192] via 172.16.0.1, 01:35:04, Serial1
>C 172.16.0.0 is directly connected, Serial1
> 193.16.0.0/30 is subnetted, 1 subnets
>O 193.16.0.0 [110/74] via 172.16.0.1, 01:35:04, Serial1
>RouterC#
>RouterC#ping 193.16.0.2
>
>Type escape sequence to abort.
>Sending 5, 100-byte ICMP Echos to 193.16.0.2, timeout is 2 seconds:
>!!!!!
>Success rate is 100 percent (5/5), round-trip min/avg/max = 28/32/36 ms
>RouterC#
>
>
>Thanks all!
>
>Hunt
>
>http://www.sold.com.au - SOLD.com.au
>- Find yourself a bargain!
This archive was generated by hypermail 2.1.4 : Tue Jul 02 2002 - 08:12:35 GMT-3