[c-nsp] OSPF(topology table vs routing table)

[Sergey Velikanov [Intelsoft]]

I've got next topology ( number between A-C this is vlan number)

A---------B
  \       /
  960   961
   \    /
     C

OSPF runs on all thee routers

router A has loopback 172.15.178.128/32
router B has loopback 172.15.178.129/32

 > router A
router ospf 1
  router-id router-id 172.15.178.128
  redistribute connected subnets
  redistribute static subnets
  network 172.15.178.152 0.0.0.7 area 10 ! router's C net
  network 172.15.178.144 0.0.0.7 area 10 ! router's B net
  default-information originate always

 > router B
  router ospf 1
  router-id router-id 172.15.178.129
  redistribute connected subnets
  redistribute static subnets
  network 172.15.178.136 0.0.0.7 area 10 ! router's C net
  network 172.15.178.144 0.0.0.7 area 10 ! router's A net

 > router C
router ospf 1
redistribute connected subnets
  redistribute static subnets
  network 172.15.178.136 0.0.0.7 area 10  ! router's B net
  network 172.15.178.152 0.0.0.7 area 10  ! router's A net

Suppose that link between A & B is down

routerC#sh ip ro | i 172.15.178.129
O E2    172.15.178.129/32 [110/20] via 172.15.178.139, 00:00:02, Vlan961
roffice2#sh ip ro | i 172.15.178.128
O E2    172.15.178.128/32 [110/20] via 172.15.178.154, 00:00:06, Vlan960

routerC#sh ip ospf database
....
   Type-5 AS External Link States
Link ID         ADV Router      Age         Seq#       Checksum Tag
172.15.178.128  172.15.178.128  460         0x8000003D 0x00B495 0
172.15.178.129  172.15.178.129  496         0x80000015 0x00F47B 0

Now I change link between A & B to up

routerC#sh ip ro | i 172.15.178.128
O E2    172.15.178.128/32 [110/20] via 172.15.178.154, 00:00:03, Vlan960
routerC#sh ip ro | i 172.15.178.129
O E2    172.15.178.129/32 [110/20] via 172.15.178.154, 00:00:04, Vlan960

routerC#sh ip ospf database
....
   Type-5 AS External Link States
Link ID         ADV Router      Age         Seq#       Checksum Tag
172.15.178.128  172.15.178.128  90          0x8000003E 0x00B296 0
172.15.178.129  172.15.178.129  90          0x80000016 0x00F27C 0


Why in topology database we see that routerC receive 172.15.178.129 & 172.15.178.128 from different routers, but in routing table next-hop for these IPs  the same (172.15.178.154 - 
router A)