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New Member

ospf area configuration

we have a router and a L3 switch in our AREA configured as below (this scenario works fine)

area x stub (router)

area x stub no summary (switch)

we inserted another L3 switch with VLANs in between and just couldnt communicate. I did configured it as the same area but DID NOT MAKE IT AS A STUB OR NO SUMMARY EITHER.

Is this causing my new L3 switch not to communicate with the old L3 and router?

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New Member

Re: ospf area configuration

Yes, the area type (e.g. stub) is sent in the E bit in hellos between routers. A neighbor will only be formed if two routers have the same E bit setting (i.e. stub or non-stub). The no-summary option is only required on the ABRs.

New Member

Re: ospf area configuration

so it does mean in my case, the old L3 switch is the ABR and the old router is an internal.

correct me if iam wrong, the way i undrstand it now is that even if the old L3 switch has the no-summary option, it should be able to communicate with my new L3 having just the stub option as below;

Old L3 stub no-summary (assumed as ABR)

old router stub

new L3 stub

thanks a lot in advance.


Re: ospf area configuration

A stub no summary is a totally stubby area, while a stub is a "normal" stub. They should work together, but I wouldn't do this--why would you want to define the area as two different types of stub areas at the same time?

All the ABR's should be configured the same way.



New Member

Re: ospf area configuration

Hi Russ,

I am just adapting to what is existing..My part is the new L3 switch to be sandwich in between the old L3 and old router and i just found that their area type differs..the switch is stub no-summary and the router is jus stub.

So am not in control of the 2.

New Member

Re: ospf area configuration

Just set the new switch to stub. This will add it to the Totally-Stub area that is in place, if the old switch is the only ABR.

New Member

Re: ospf area configuration

Yes you are correct, the key thing is to have all areas within an area configured as stub, if you want stub functionality. To confirm which one is your ABR, please do a sh ip ospf and it will be displayed.