- Blue, 1500 points or more
Please view the attached drawing before you read on and you may want to leave it open to refer to it.
Anyway, here is the scoop.
The OSPF area represents our Australia network.
Routers SING and JAPAN are OSPF ASBRs that redistribute OSPF-learned routes into BGP.
Both the SING and JAPAN routers form iBGP neighborships with both FMC and ECC in the United States.
So, FMC learns OSPF Australia routes through iBGP from both SING and JAPAN.
And ECC learns OSPF Australia routes through iBGP from both SING and JAPAN, too.
Right now, both FMC and ECC routers favor the SING router as the "next hop."
The reason is that all things being equal, the SING router carries a better IGP metric into its BGP advertisements than the JAPAN router does.
So, if one does a "sh ip bgp 188.8.131.52" (this is an Australia network) in the FMC and ECC routers, they will both show that they have learned 2 routes through iBGP, one from SING and one from JAPAN, but the SING router carries an IGP (OSPF) metric of, say, 330, while the JAPAN router advertises an IGP metric of 445. Therefore, the SING route is favored, so the FMC and ECC routers place the SING-learned iBGP routes in their BGP table.
<i>ecc#sh ip bgp 184.108.40.206
BGP routing table entry for 220.127.116.11/29, version 31730939
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Advertised to update-groups:
18.104.22.168 (metric 1466112) from 22.214.171.124 (126.96.36.199)