OSPF Process ID

Hi,

Are there instances where they are more than 1 process id on the same ospf router?
If so, why will someone do that?

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EdTheLad

Yes, when you want to isolate two routing domains, rather than using vrf's.

dppagc

So there are 2 ways of doing the same thing?

But I thought vrf is necessary at PE routers to distinguish between customer routes?

pevangel

With VRFs, the tables are separate inside a single router. When you have two OSPF processes, the two processes will have separate databases but all routes will be in the same routing table.

james43026

As pevangel has said, you could have 10 instances of OSPF running on a router, and they would all populate the global routing table, all with a separate OSPF database. While using VRF's for the same thing would yield 10 different route tables, that would appear to be physically separate from eachother.

And yes VRF is used by service providers in their network for layer 3 VPNs, usually with either a MPLS backbone, or a MP-BGP backbone connecting said PE routers together. VRF isn't used for layer 2 VPNs though.

dppagc

Ok I understand the concept of VRF but it doesnt answer the original question.
Why should someone create more than 1 instance of an OSPF process if they populate the same routing table?

What is the command to show that they are in separate databases?

EdTheLad

"show ip ospf database" will show the two process databases
"show ip ospf 1 database" or "show ip ospf 2 database"

As an example, within an organization security department want to utilize the core infrastructure i.e. routers but use there own cards. You can create infrastructure links separate on each router which are utilized only by the security department. 2 ospf processes are configured, one for regular core and 1 for security. All security routes are isolated, no redistribution, no vrf required, no security issue with vrf leak. Shared RIB, but no default route, complete isolation on the same physical router without relying on software vrf.

dppagc

Hi,

do you want elaborating on the sentence "use their own cards" ?

EdTheLad

Typically core routers are modular, i.e. have pluggable modules i.e. NCS, CRS, ASR, 7600, 6500