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.
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