- Blue, 1500 points or more
I have a question regarding BGP advertisements.
I have an iBGP peer whose parameters are the following:
router bgp 65000
timers bgp 15 45
neighbor AS65000 peer-group
neighbor AS65000 remote-as 65000
neighbor AS65000 password 7 02000B490F0408310C
neighbor AS65000 update-source Loopback0
neighbor AS65000 next-hop-self
neighbor AS65000 route-map Ford-Internal-Routes-Only out
neighbor AS65000 maximum-prefix 50000 80
neighbor 184.108.40.206 peer-group AS65000
According to this config, the next-hop that should be advertised by this router to iBGP peer 220.127.116.11 is itself.
But thats not the case. This router is acting in the classic BGP fashion, where it learns of a prefix through eBGP and passes the prefix on to its iBGP neighbor with the originating router as the next-hop.
ecc#sh ip bgp nei 18.104.22.168 advertised-routes
BGP table version is 34095654, local router ID is 22.214.171.124
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
*> 0.0.0.0 126.96.36.199 0 32768 i
*> 188.8.131.52/32 184.108.40.206 20 0 65300 ?
*> 220.127.116.11/28 18.104.22.168 20 0 65300 ?
ecc#sh ip bgp 22.214.171.124
BGP routing table entry for 126.96.36.199/32, version 30991629
Paths: (3 available, best #2, table Default-IP-Routing-Table)
Advertised to update-groups:
2 3 4 5
188.8.131.52 from 184.108.40.206 (220.127.116.11)
Origin incomplete, metric 20, localpref 100, valid, external
18.104.22.168 from 22.214.171.124 (126.96.36.199)
Origin incomplete, metric 20, localpref 100, valid, external, best
188.8.131.52 (metric 130816) from 184.108.40.206 (220.127.116.11)
Origin incomplete, metric 20, localpref 100, valid, internal
ecc#sh ip ro 18.104.22.168
Routing entry for 22.214.171.124/32
Known via "bgp 65000", distance 20, metric 20
Tag 65300, type external
Last update from 126.96.36.199 1w5d ago
Routing Descriptor Blocks:
* 188.8.131.52, from 184.108.40.206, 1w5d ago
Route metric is 20, traffic share count is 1
AS Hops 1
Route tag 65300
So, notice that ECC learned of this 4.x.x.x prefix from an eBGP neighbor with a next-hop of 220.127.116.11, and it is that next-hop that it passes on to its iBGP neighbor 18.104.22.168.
What am I missing -- besides a brain?
You won't be able to see the attribute modified on the source router. The attribute is modified as it leaves the router. To verify your suspicion, I recommend checking the receiving router.
Same logic applies when setting an as path-prepend. You don't see the as-path added on the advertised routes, right?