I am working in an ISP which is one of the biggest ISP in my country. Currently my company is an ISP as well as IIG. In our ISP we have thousand of customer and in our IIG there are many ISP are connected with us. In the recent time I have faced a problem for the customer who have their own IPv4 resources and they are connected with us through our ISP network. Please see the below network diagram:
Customer has their own IP resources which is 22.214.171.124/24 and we have configured eBGP multihop BGP with customer router to ISP core router as the customer is not directly connected with ISP core router. Now the problem is prefix which I am receiving from customer in ISP core router is best and valid but in IIG Aggregation Router customer prefix is only valid not best. As a result our IIG Core router not receving that prefix from IIG Aggregation Router and globally customer prefix is not reachable through us. Please see the below BGP receive route for your kind reference:
BGP receive route from ISP Core Router
>sh ip bgp neighbors 126.96.36.199 ro BGP table version is 1346629, local router ID is 188.8.131.52 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 *> 184.108.40.206/24 220.127.116.11 0 0 58917 i
BGP receive route from IIG Aggregation Router
#sh ip bgp neighbors 18.104.22.168 ro
BGP table version is 414210727, local router ID is 22.214.171.124 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
Next hop is reachable from IIG aggregation router and here is ping reply from IIG aggregation router :
Aggre-1#ping 126.96.36.199 source 188.8.131.52 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 184.108.40.206, timeout is 2 seconds: Packet sent with a source address of 220.127.116.11 !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms
No route-map applied to thr peer from where I am learning the prefix.
Please post "sh ip bgp 18.104.22.168/24" from IIG Core as it is beign advertised by IIG Agg to the IIG core, it's just not best. That show output from IIG core does not help unless I have it backwards somehow.
the next-hop may not be reachable form the IIG core, and you performed a ping test from IIG Agg which has not issues as per you outputs.
#sh ip route 22.214.171.124 Routing entry for 126.96.36.199/24 Known via "bgp 58601", distance 200, metric 0 Tag 9498, type internal Last update from 188.8.131.52 23:22:13 ago Routing Descriptor Blocks: * 184.108.40.206, from 220.127.116.11, 23:22:13 ago Route metric is 0, traffic share count is 1 AS Hops 7 Route tag 9498 MPLS label: none
The best route on IIG Aggregation router is received via an IBGP neighbor. If the BGP peering IIG Aggregation and IIG Core is iBGP this route will not be sent to the IIG Core , thats the BGP Split Horiozon rule.
And Like Rolf said , to get this traffic engineering done you should contact some of your senior colleagues, as its quite tough to suggest changes on your production network which could be quite complex.
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