Hey all, I'm probably missing some fairly simple concept here. I have setup
4 routers as follows:-
RTB
/
RTD --- RTA
\
RTC
Both RTB & RTC are connected (via Eth) to a network called 172.17.1.0 /24.
RTA & RTD are both in AS2
RTB & RTC are both in AS1
The connection between RTA & RTD is via Ethernet
RouterA#sh ip bgpBGP table version is 9, local router ID is 25.25.25.2
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
*> 10.1.1.0/30 10.1.1.2 0 0
1 i
* 10.1.2.2 0
1 i
*> 10.1.2.0/30 10.1.1.2 0
1 i
* 10.1.2.2 0 0
1 i
*> 25.25.25.0/24 0.0.0.0 0
32768 i
*> 172.17.1.0/24 10.1.1.2 0 0 1
i
* 10.1.2.2 0 0
1 i
RouterA#sh running-config
router bgp 2
network 25.25.25.0 mask 255.255.255.0
neighbor 10.1.1.2 remote-as 1
neighbor 10.1.2.2 remote-as 1
neighbor 25.25.25.1 remote-as 2
maximum-paths 6
When I lookup RTD's BGP table (shown below), for the route 172.17.1.0/24,
instead of via 10.1.1.2 or 10.1.2.2, it is 25.25.25.2. Ok - here's what I'm
confused about. Since I thought that in EBGP peering, the next hop is
usually the IP address of the neighbor that announced the route, but IBGP
peering preserve the Next-hop attribute learned from EBGP peers. So in the
case, if I haven't use next-hop-self on RTA, I would think the EBGP next hop
in RTD's BGP table would be either 10.1.1.2 or 10.1.2.2, but why is the EBGP
next-hop is 25.25.25.2?
RouterD#sh ip bgp
BGP table version is 6, 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
*>i10.1.1.0/30 25.25.25.2 0 100 0 1
i*>i10.1.2.0/30 25.25.25.2 100 0 1
i*>i25.25.25.0/24 25.25.25.2 0 100 0 1 i
*>i172.17.1.0/24 25.25.25.2 0 100 0 1 i
Thanks,
H.
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