I have BGP multihoming with two cisco routers. Each router has its own ISP and announce our AS with our /24 network to the internet.
My issue is between those two routers :
Router A, routing table looks like :
BGP table version is 9622808, local router ID is 10.100.100.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path
*>i 1.0.0.0/24 10.100.100.3 10041 150 0 175 15169 i
* 192.168.200.1 0 0 800 15169 i
Router B, routing table looks like :
router#sh ip bgp
BGP table version is 10261936, local router ID is 192.168.1.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path
*> 1.0.0.0/24 192.168.1.1 10041 150 0 175 15169 i
Router A
#sh ip bgp 1.0.0.0
BGP routing table entry for 1.0.0.0/24, version 9124223
Paths: (2 available, best #1, table default)
Multipath: eBGP
Not advertised to any peer
Refresh Epoch 1
175 15169
10.100.100.3 from 10.100.100.3 (192.168.1.1 )
Origin IGP, metric 10041, localpref 150, valid, internal, best
rx pathid: 0, tx pathid: 0x0
Refresh Epoch 1
8220 15169
192.168.200.1 from 192.168.200.1 (212.74.90.252)
Origin IGP, metric 0, localpref 100, valid, external
Community: 538770940 538771322
rx pathid: 0, tx pathid: 0
Router B
#sh ip bgp 1.0.0.0
BGP routing table entry for 1.0.0.0/24, version 9772009
Paths: (1 available, best #1, table default)
Multipath: eBGP
Advertised to update-groups:
15
Refresh Epoch 1
175 15169
192.168.1.1 from 192.168.1.1 (38.28.4.10)
Origin IGP, metric 10041, localpref 150, valid, external, best
Community: 11424364 11425276
rx pathid: 0, tx pathid: 0x0
Router B
#sh ip bgp summary
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
10.100.100.2 4 48020 748914 2167278 10705132 0 0 2w4d 3350
192.168.1.1 4 175 2591251 29738 10705000 0 0 2w4d 509418
My issue is that Router B has only one Next Hop for the 1.0.0.0/24 (this is an example).
I am expecting that router B has another Next Hop to router A.
Router A is showing both Next hop as expected.
This issue has serious impact, If we lose router B as the preferred router we lose Internet, since it is not able to route traffic through router A.
Best Answer
In your case, B should not have route from A because B itself is declaring its learned route as the best route and disseminating this info via iBGP.
Router A can't advertise its eBGP learned 1.0.0.0/8 to B because it's not the best route. The best route for A is the one it learned via iBGP from B and iBGP routes can't be re-advertised.
Both of the eBGP routers are learning networks from both ISPs. When ISP for B fails, A eBGP routes will become eligible to be sent to B.
HTH.