Any advantage to multiple OSPF areas

Unanswered Question
Jul 14th, 2011

Currently the link between Site A and Site B is Dot1Q and carries the vlans on the Site B side, but only a couple on the Site A side.  It is all on OSPF area, and the link between the two sites will be changed from Dot1Q to routed.


My question is whether or not to keep it as on OSPF area or use two areas - one for each site.  Maybe the biggest criteria will be avoiding routing/recovering from loops and recovering from spanning tree loops (site A has some equipment old enough to be potential problems in that respect)  Any thoughts and advice will be very helpful.



I have this problem too.
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p.mcgowan Thu, 07/14/2011 - 08:51

if you make 2 areas, you will need to configure both area's on the main routers at site a and site b. with OSPF as soon as you add more than one area, you need to add area border routers, ABR's are used to route between the 2 seperate area's

Richard Burts Thu, 07/14/2011 - 12:03


From your description I think that there might be some advantage in configuring multiple OSPF areas as you change to a routed link between the sites. Configuring multiple OSPF areas helps eliminate disruption in one area from problems in the other area.

Based on your drawing I can think about two possible approaches. You could configure two areas. As noted above one of the areas must be area 0 and the other area could be whatever you want to number it. The other possibility could be three areas. You could make the area 0 to be the routers that connect between sites and have another area for siteA and another area for siteB. Either approach should work but in terms of limiting the failure domain I like the 3 area approach.



Marwan ALshawi Thu, 07/14/2011 - 18:29

just to add to Rick post

you might consider having stub or NSSA areas with the remote sites to reduce the amount of route being sent to the remote sites over the WAN and have more control over the route being passed between differnt areas and also consider the advertisement of the default as i can see you have some local Internet connections

good luck

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