Help Migrating to New OSPF Model

boshardy1 · ‎09-06-2006

We are looking to move away from a single area ospf design to multiple areas. Right now we are using just area 1. We would also like to do better summarization, authentication, etc.

I was thinking we could make the transition smoother by running two OSPF processes on our routers, and moving things across as we migrate. For example here is router A

router ospf 100

log-adjacency-changes

redistribute static

network 10.255.1.0 0.0.0.255 area 1

network 10.255.2.0 0.0.0.255 area 1

network 10.255.3.0 0.0.0.255 area 1

network 10.255.255.254 0.0.0.0 area 1

network 10.1.0.0 0.0.255.255 area 1

My plan was to add a process because I am assuming that authentication is enabled on a process level and once turned on I would break routing unless I have everything configured. So I would add the following configs:

router ospf 100

log-adjacency-changes

redistribute static

network 10.255.1.0 0.0.0.255 area 1

network 10.255.2.0 0.0.0.255 area 1

network 10.255.3.0 0.0.0.255 area 1

router ospf 875

log-adjacency-changes

network 10.1.0.0 0.0.255.255 area 0

area 0 authentication message-digest

Now my questions

1). If I want to summarize routes coming into the newly created area 0 from area 1 do I put the area X range commands on that process (100) or 875 (area 0).

2). Would I redistribute routes between the two processes?

Thanks

jackyoung · ‎09-06-2006

You require to redistribute the routes between two processes, but beware to avoid to redistribute the route back from original process. Apply route-map during the reditribution to avoid it.

Once you resdistributed the routes, you can summarize it in new process.

Moreover, it is correct that always use area 0 to be the backbone area.

But why require two process ? And not simply to change 10.1.1.0/16 to area 0 then you don't need redistribution. You are correct that enable the authentication of area 0 but it won't affect area 1 because there is no such authentication command. So it won't affect the area 1 user until you enable the authentication at area 1 too. I belive the authentication modication is simplier than control routes between redistribution.

I suggest you take a trail run at lab before actual migration.

Please check below for the OSPF design guide :

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml

Hope this helps.

anton.elita · ‎09-06-2006

Hi,

it would be much easier to change authentication than running two ospf processes. Authentication can be implemented per-area, but overriden with per-interface configuration (ip ospf authentication in interface config mode)

sample example and summary to ospf authentication you could find on http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a0080094069.shtml

regards,

anton