OSPF design / best practice ?

[mwilson]

I've been thinking about ospf design which led me to the following question.  

Should area 0 be extended out? or should other areas be brought in?  

Say you have 10 sites.  Each with an ospf area.   P2p connection to each site.   Should that interface extend area 0 to them?  Or should interface bring remote area into area 0?  

Any thoughts are appreciated.

[Julio E. Moisa]

Hi

You could keep different areas, one for each site, but they always need to be connected to the Area 0. Now a good practices is configure incremental SFP (isfp) under the router ospf <process ID>, so each change will be kept into each area, so it will not affect the OSPF computation. In few word the STP will not recompute once the LSA Type 1 and 2 are advertising a change. 

The following link could be useful:

https://supportforums.cisco.com/document/98446/ospf-design-best-practices

:-)

[Joseph W. Doherty]

Good question - I think it's an "it depends" answer.

As general recommendation is not to have an ABR host many different areas.  If all you sites were connected to the same hub router, that router would host 11 different areas.  However, if the ABR is remote, each remote site ABR would only host 2 areas.

Conversely though, if your ABRs are remote, the p2p link would need may need to deal with more OSPF LSA traffic than if the ABR was as the hub site.  Also if the ABR was as the hub site, a WAN link up/down could be filtered out from impacting area 0.

The question, and a good answer, also becomes more complicated depending on the kind of non-zero areas and whether you'll have any redundancy paths to the non-zero areas.