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 220.127.116.11 peer-group AS65000
According to this config, the next-hop that should be advertised by this router to iBGP peer 18.104.22.168 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 22.214.171.124 advertised-routes
BGP table version is 34095654, local router ID is 126.96.36.199
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
*> 0.0.0.0 188.8.131.52 0 32768 i
*> 184.108.40.206/32 220.127.116.11 20 0 65300 ?
*> 18.104.22.168/28 22.214.171.124 20 0 65300 ?
ecc#sh ip bgp 126.96.36.199
BGP routing table entry for 188.8.131.52/32, version 30991629
Paths: (3 available, best #2, table Default-IP-Routing-Table)
Advertised to update-groups:
2 3 4 5
184.108.40.206 from 220.127.116.11 (18.104.22.168)
Origin incomplete, metric 20, localpref 100, valid, external
22.214.171.124 from 126.96.36.199 (188.8.131.52)
Origin incomplete, metric 20, localpref 100, valid, external, best
184.108.40.206 (metric 130816) from 220.127.116.11 (18.104.22.168)
Origin incomplete, metric 20, localpref 100, valid, internal
ecc#sh ip ro 22.214.171.124
Routing entry for 126.96.36.199/32
Known via "bgp 65000", distance 20, metric 20
Tag 65300, type external
Last update from 188.8.131.52 1w5d ago
Routing Descriptor Blocks:
* 184.108.40.206, from 220.127.116.11, 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 18.104.22.168, and it is that next-hop that it passes on to its iBGP neighbor 22.214.171.124.
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?