[c-nsp] BGP next hops in BGP not in IGP

[Kamal Dissanayaka]

HI All,

As my knowledge, BGP next hop needs to be in IGP in order to get BGP routes
in routing table.
It looks like, it may have changed ?  BGP routes populate in routing table
when the next-hp route is learned through BGP.

I tried some googling but I cannot get definite answer.

here is the scenrio

Router A (18162) 172.18.112.41---- 172.18.112.40 Router B (65001)
172.18.112.37 --- 172.18.112.38 Router C (65001)

On router C,

Subnet 172.18.112.40/30  is learned through IBGP, As far as I remeber on my
old school this subnet should be learned through IGP to work properly.

Router C# sh ip route  172.18.112.41
Routing entry for 172.18.112.40/30
  Known via "bgp 65001", distance 200, metric 0, type internal
  Last update from 172.18.112.37 3w3d ago
  Routing Descriptor Blocks:
  * 172.18.112.37, from 172.18.112.37, 3w3d ago
      Route metric is 0, traffic share count is 1
      AS Hops 0

However other routes advertised from Router A is on routing table of Router
C. Is it something expected ??

Router C#sh ip route bgp
     172.18.0.0/16 is variably subnetted, 4 subnets, 2 masks
B       172.18.28.52/30 [200/0] via 172.18.112.41, 3w3d
B       172.18.20.24/29 [200/0] via 172.18.112.41, 3w3d
B       172.18.112.40/30 [200/0] via 172.18.112.37, 3w3d
     172.21.0.0/16 is variably subnetted, 7 subnets, 3 masks
B       172.21.25.0/24 [200/0] via 172.18.112.41, 2w6d
B       172.21.17.0/24 [200/0] via 172.18.112.41, 2w6d
B       172.21.14.0/23 [200/0] via 172.18.112.41, 3w3d


Router C #show ip bgp  172.21.17.0/24
BGP routing table entry for 172.21.17.0/24, version 48
Paths: (2 available, best #2, table Default-IP-Routing-Table)
  Advertised to update-groups:
     2
  18162 64634, (received & used)
    10.201.177.25 from 10.201.177.25 (10.201.177.17)
      Origin IGP, localpref 100, valid, external
  18162 64634, (received & used)
    172.18.112.41 from 172.18.112.37 (172.18.112.37)
      Origin IGP, localpref 150, valid, internal, best
      Extended Community: RT:18162:2000430014


Best Regards

Kamal