Hunt,
Read this link and think about your scenario for a moment. "What
is the problem to be solved?"
http://www.cisco.com/warp/public/459/bgpfaq_5816.shtml#12
Then read this link. The emphasis here is that although RTA, RTB, RTC, RTD,
and RTE are in the same confed AS1, RTB and RTC,
and RTD and RTE, are in separate sub-ASs within the AS. What dies that
mean? If RTB and RTD are propagating iBGP route information
to RTC and RTE respectively then, the only way for these routes to be sync'd
is by NLRI(through an IGP), route-reflectors or by using
the "cisco-specific knob - no sync". By, using the "no sync" you're
allowing BGP to overlook the native requirements of the protocol, which
will install the route into the RIB.
http://www.cisco.com/warp/public/459/16.html#A23.0
You might want to also look at rfc1965 which laid the foundation for the use
of confederation within
BGP, however this is superceded by rfc3065. Of course there are a number of
other options that could be used to achieve full mesh
within an AS. Some of those options include rfc1966, and rfc1863
http://www.ietf.org/rfc/rfc1863.txt
http://www.ietf.org/rfc/rfc1966.txt
HTH
Nigel
----- Original Message -----
From: "Hunt Lee"
To:
Sent: Sunday, June 16, 2002 6:42 AM
Subject: BGP w/ no synchronization [7:46707]
> 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
> 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
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=46709&t=46707
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