ospf sanity check...

this morning i thought i'd build the ipv6 layer 3 topology from the ccnp topology...

and here it is...

looking at it i was suddenly dumbfounded at the peculiar AS #6... i had a wtf moment about something i couldn't have possibly missed on the way through...

this was profoundly disturbing...  my initial thought was they wanted to match the process id's within the areas... what else?

hence the sanity check... so i dug, because in this crazy business it is easy to be a victim of misinformation, even from the horse's mouth...

 http://www.cisco.com/en/US/tech/tk365/technologies_q_and_a_item09186a0080094704.shtml


OSPF, unlike Border Gateway Protocol (BGP) or Enhanced Interior Gateway Routing Protocol (EIGRP), does not check the process number (or autonomous system number) when adjacencies are formed between neighboring routers and routing information is exchanged. The only case in which the OSPF process number is taken into account is when OSPF is used as the routing protocol on a Provider Edge to Customer Edge (PE-CE) link in a Multiprotocol Label Switching (MPLS) VPN. PE routers mark OSPF routes with the domain attribute derived from the OSPF process number to indicate whether the route originated within the same OSPF domain or from outside it. If the OSPF process numbering is inconsistent on PE routers in the MPLS VPN, the domain-id OSPF mode command should be used to mark that the OSPF processes with different numbers belong to the same OSPF domain.
This means that, in many practical cases, you can use different autonomous system numbers for the same OSPF domain in your network. However, it is best to use consistent OSPF-process numbering as much as possible. This consistency simplifies network maintenance and complies with the network designer intention to keep routers in the same OSPF domain.

this is big... this smacks of a best practice... not sure about you but i invariably use 1... and there you have it...

it bears repeating...
The only case in which the OSPF process number is taken into account is when OSPF is used as the routing protocol on a Provider Edge to Customer Edge (PE-CE) link in a Multiprotocol Label Switching (MPLS) VPN. PE routers mark OSPF routes with the domain attribute derived from the OSPF process number to indicate whether the route originated within the same OSPF domain or from outside it.

in this case the process-id is the AS and the domain indicator...

it is safe to believe that in an ospf topology it is important to match the process-id with the indicated, so called AS number...