OSPF - one interface in multiple processes

[radugpopa]

Hi,

I have to configure two Cisco 3925 routers using OSPF. I have defined three different processes in order to isolate dome internal LANs from others. In order to share routes the routers are connected to each other via 172.17.1.x network beloging to area 0. From theory I understood that in order to act as inter-area routers I have to use the area 0 interface in each process. The problem is that even if I define it in multiple processes it seems that it is used only in one:

router ospf 1
log-adjacency-changes
network 172.17.1.2 0.0.0.0 area 0
network 172.16.115.0 0.0.0.255 area 0
network 192.168.51.0 0.0.0.255 area 3
network 192.168.52.0 0.0.0.255 area 3
network 192.168.53.0 0.0.0.255 area 3
network 192.168.99.0 0.0.0.255 area 3
!
router ospf 2
log-adjacency-changes
network 172.17.1.2 0.0.0.0 area 0
network 172.16.114.0 0.0.0.255 area 1
network 192.168.55.0 0.0.0.255 area 1
!
router ospf 3
log-adjacency-changes
network 172.17.1.2 0.0.0.0 area 0
network 172.16.113.0 0.0.0.255 area 0
network 192.168.54.0 0.0.0.255 area 2

My question is: can an interface be used in multiple OSPF processes?

Thank you!

[Peter Paluch]

Hello Radu,

In OSPF for IPv4, an interface can be a part of a single OSPF process only. The OSPF packets do not have any identification into which process they belong, and if an interface was active in several OSPF processes, the OSPF packets sent out that interface could not be properly distinguished and sorted among process instances. The OSPFv3 for IPv6 includes a support for running multiple instances over a single interface but as of now, the OSPFv3 supports only IPv6 and so it would not be helpful to you.

Could you perhaps post a drawing of your network so we can better understand what are you trying to accomplish? Perhaps you could interconnect your two routers with a set of subinterfaces (802.1Q VLANs or similar) under one physical interface, each one being assigned to a single OSPF process only.

Best regards,

Peter