From: Peter van Oene (pvo@xxxxxxxxxxxx)
Date: Wed Jul 10 2002 - 12:34:58 GMT-3
This only works because B is using a connected interface toward RTC for the
next hop on 172.16.1/24. I assume you do not have a loopback on
RTB? Putting the ebgp /30 net into BGP is nice and will allow you to
resolve EBGP next hops, but how do you resolve the next-hop for the /30 you
just put into BGP? Again, without an IGP, distant routers will not be able
to post this route and therefore not resolve the original BGP route
either. For example, if RTB had a loopback address of 172.16.1.1/32, it
would set the next-hop on 172.17.1/24 to 172.16.1.1 which RTC would not
know about and thus C would neither post it nor the 199 route.
At 11:53 PM 7/10/2002 +1000, Hunt Lee wrote:
>Hi Group,
>
>199.172.1.0 / 24 --- RTA --- RTB --- RTC
>
>RTA's interface - 172.17.1.2 (connecting to RTB)
>RTB's interface - 172.17.1.1 (connecting to RTA)
>RTB's interface - 10.1.1.1 (connecting to RTC)
>RTC's interface - 10.1.1.2 (connecting to RTB)
>
>RTA is in AS 1
>RTB & RTC are both in AS 2
>
>I understand that for a router to learn and install an IBGP route
>from an IBGP neighbor, it will need either "no sync" command or
>learnt via any IGP. But for the BGP route's next-hop reachability, I
>have searched on Cisco books & CCO website, but they only said either
>advertised the next-hop to the IBGP router (in this case, RTC) with
>IGP routes, or use "next-hop-self" command (on RTB). However, I
>found that if I advertise the next-hop reachability (the
>172.17.1.0/24 subent) via BGP's network command, it would also work.
>Is this ok to use?? Is there any gotcha on this?? I just thought it
>is pretty handy to just use BGP, without relying on any IGP.
>
>
>RouterB#sh ip bgp
>BGP table version is 4, local router ID is 192.168.0.1
>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
>*> 10.1.1.0/30 0.0.0.0 0 32768 i
>*> 172.17.1.0/24 0.0.0.0 0 32768 i
>*> 199.172.1.0 172.17.1.2 0 0 1 i
>
>RouterB#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, ia - IS-IS
>inter
>area
> * - candidate default, U - per-user static route, o - ODR
> P - periodic downloaded static route
>
>Gateway of last resort is not set
>
> 172.17.0.0/24 is subnetted, 1 subnets
>C 172.17.1.0 is directly connected, Ethernet0
> 10.0.0.0/30 is subnetted, 1 subnets
>C 10.1.1.0 is directly connected, Serial0
>B 199.172.1.0/24 [20/0] via 172.17.1.2, 01:34:38
>C 192.168.0.0/24 is directly connected, Loopback0
>RouterB#
>
>And at RTC, it would be able to reach 199.172.1.0 /24 via next hop of
>172.17.1.2, which in turn is reached via 10.1.1.1.
>
>RouterC#sh ip bgp
>BGP table version is 4, local router ID is 172.16.3.1
>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
>*>i10.1.1.0/30 10.1.1.1 0 100 0 i
>*>i172.17.1.0/24 10.1.1.1 0 100 0 i
>*>i199.172.1.0 172.17.1.2 0 100 0 1 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
>
> 172.17.0.0/24 is subnetted, 1 subnets
>B 172.17.1.0 [200/0] via 10.1.1.1, 00:26:57
> 172.16.0.0/24 is subnetted, 2 subnets
>C 172.16.2.0 is directly connected, Loopback1
>C 172.16.3.0 is directly connected, Loopback0
> 10.0.0.0/30 is subnetted, 1 subnets
>C 10.1.1.0 is directly connected, Serial0
>B 199.172.1.0/24 [200/0] via 172.17.1.2, 00:25:57
>RouterC#
>
>
>Any ideas will be greatly appreciated.
>
>Thanks!!!
>
>H.
>
>
>
>http://www.sold.com.au - SOLD.com.au
>- Find yourself a bargain!
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