CSR14
router bgp 100
address-family ipv4
network 100.14.14.14 mask 255.255.255.255
CSR15#debug bgp ipv4 unicast update
BGP(0): 100.9.15.9 rcvd UPDATE w/ attr: nexthop 100.9.15.9, origin i, merged path 100, AS_PATH
BGP(0): 100.9.15.9 rcvd 100.14.14.14/32
BGP(0): Revise route installing 1 of 1 routes for 100.14.14.14/32 -> 100.9.15.9(global) to main IP table
BGP(0): (base) 100.13.15.13 send UPDATE (format) 100.14.14.14/32, next 100.13.15.15, metric 0, path 100
BGP(0): 100.13.15.13 rcvd UPDATE w/ attr: nexthop 100.13.15.13, origin i, merged path 100, AS_PATH
BGP(0): 100.13.15.13 rcvd 100.14.14.14/32
BGP(0): 100.9.15.9 rcvd UPDATE w/ attr: nexthop 100.9.15.9, origin i, merged path 100, AS_PATH
BGP(0): 100.9.15.9 rcvd 100.14.14.14/32...duplicate ignored
CSR15#show bgp ipv4 unicast summary
BGP router identifier 100.15.15.15, local AS number 15
BGP table version is 2, main routing table version 2
1 network entries using 248 bytes of memory
2 path entries using 240 bytes of memory
1/1 BGP path/bestpath attribute entries using 256 bytes of memory
1 BGP AS-PATH entries using 24 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 768 total bytes of memory
BGP activity 1/0 prefixes, 2/0 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
100.9.15.9 4 100 55 55 2 0 0 00:46:31 1
100.13.15.13 4 100 41 44 2 0 0 00:37:45 1
CSR15#show bgp ipv4 unicast
BGP table version is 2, local router ID is 100.15.15.15
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
* 100.14.14.14/32 100.13.15.13 0 100 i
*> 100.9.15.9 0 100 i
CSR15#show bgp ipv4 unicast 100.14.14.14
BGP routing table entry for 100.14.14.14/32, version 2
Paths: (2 available, best #2, table default)
Advertised to update-groups:
2
Refresh Epoch 1
100
100.13.15.13 from 100.13.15.13 (100.13.13.13)
Origin IGP, localpref 100, valid, external
rx pathid: 0, tx pathid: 0
Refresh Epoch 1
100
100.9.15.9 from 100.9.15.9 (100.9.9.9)
Origin IGP, localpref 100, valid, external, best
rx pathid: 0, tx pathid: 0x0
There are 2 peerings via eBGP to AS 100. But only the peering via IOS9, 100.9.15.9, is the best path. The reason for this is that the IOS9 peering came up first and is the oldest peering therefore it becomes the best path.
