R1 received 220.127.116.11/24 as an ebgp update with next hop .2 .3 .4 as expected but why that`s not happened with 18.104.22.168/24 and 22.214.171.124/24 and 126.96.36.199/24
why i see 188.8.131.52 3 times ? 184.108.40.206 3 time ?same next hop
R3 is going to advertise 220.127.116.11/24 to R1 with next hop 10.1.12.3 only one time why R3 advertise it 3 times to R1 ?because i see the next hop 10.1.12.3 3 times
That looks rather buggy to me. On R1, when you issue the command, “show ip bgp 18.104.22.168/24” do you actually see three entries? Is there anything that makes each one different from the others?
sir,do you think it`s a bug ?
Okay…here’s what’s going on (I’ll just explain it for the 22.214.171.124/24 prefix but the same principle applies for 126.96.36.199/24 and 188.8.131.52/24)
You have a BGP “network 184.108.40.206 mask 255.255.255.0” statement in R2. So this means that R2 will advertise this prefix:
—a. via eBGP directly to R1
—b. via iBGP directly to R3
—c. via iBGP directly to R4
When R2 sends this prefix via eBGP to R1 it sets the next-hop attribute to itself (10.1.12.2)
When R3 receives the iBGP update from R2, R3 then transmits this as an eBGP update to R1. Because of the “third party next-hop” rule R3 does NOT change the next-hop to itself but instead leaves the next-hop as 10.1.12.2. This is because R3 knows that R1 and R2 are in the same subnet.
The same thing I described above happens on R4. It receives the route via R2 as iBGP and re-transmits it to R1 as eBGP. It does not change the next-hop because of the “Third party next-hop” rule.
For more info on that rule, please see this INE Blog posting: