OSPF Design Best Practice

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Mar 30th, 2008
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I have network consists of HQ and 50 Branches .I'd like to use OSPF .the HQ will be in Area 0 .My question is that should i put each beanch in a separate area (Non Area 0) or i should put all the branches in one non area zero .

Pls advice

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ruwhite Sun, 03/30/2008 - 06:28
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What size routers, how many routes, what size links, etc? Typically, you should be okay with all 50 spokes in a single area, unless they are really small routers, and you have a lot of routes, and you have tight convergence requirements. I would make the area you put these spokes in the "most stub possible." A totally stubby area is going to be best, but, failing that, a stubby area, or a not-so-stubby area. Reducing the information flowing between area 0 and the hub and spoke area will help keep things stable on both sides when there are major outages of any sort.


:-)


Russ

welcomeccie Sun, 03/30/2008 - 07:40
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the no of branches are about 45 and each beanch has 1 router that connected to the HQ routers (2) by 2 links .

I think to put each beanch with its 2 links in one area and do Totaly stubby area but i don't know if it is the optimum or not

minumathur Sun, 03/30/2008 - 06:38
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Hi


Basically to reduce the LSA advertisment is OSPF protocol is key point. so if you imeplement all the branch office in single area that will increase your LSA Advertisment in backbone. so my suggestion is to implement "Not-So-Stub area " technology this will help to reduce you LSA advertisment.


I hope this will clear your doubts.


-M

Richard Burts Sun, 03/30/2008 - 15:05
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M


Not So Stubby Area is a very good thing if there is a need to redistirbute routes into OSPF. But I have not seen anything from the original poster that indicates a need for redistribution into OSPF. If there is no need for redistribution then I believe that Totally Stubby areas are better for the network, if I understand the network environment correctly.


I worked with a customer whose network environment was very similar to what is described: there was a HQ with 2 core routers, there were many remotes with each remote dual connected back to HQ, most remotes were in separate areas. They were running the remote areas as normal OSPF areas and were experiencing some performance issues. When they changed all the remote areas to Totally Stubby areas there was a marked improvement in the operation of their network. Given what I think I understand of the network described here I would suggest that each remote in its own area and each remote area defined as Totally Stubby is a pretty optimum way to do it.


HTH


Rick

welcomeccie Mon, 03/31/2008 - 01:51
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Thanks for your reply.If i create an area for each Remote site that means that i will create about 45 areas .Waht do u think about that

Richard Burts Mon, 03/31/2008 - 05:25
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I think that could work ok - especially if you make each remote area to be totally stubby. It is not a typical OSPF design. But it works fine.


HTH


Rick

Richard Burts Mon, 03/31/2008 - 08:28
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Optimum in terms of what? There is not any single "optimum" design that fits everywhere. Each design must consider the environment of the network for which it is the design. As Russ White indicated some of the variables include what kind of routers are you running, how many routes (prefixes) on each router and how many routes in the network. You may also need to consider the convergence requirements that Russ mentioned. I believe that it is also important to consider what the traffic patterns are also (is the traffic almost always from a spoke to the hub and response, or is there significant spoke to spoke traffic?


Russ suggested that you would probably be fine in having a single area for the remote spoke routers. And I agree with that. And from the standpoint of simplicity that would be optimum. I also suggested that there would be some potential benefit in reducing the number of LSAs flooded to each remote spoke if you put each remote spoke into its own area and made all the remote areas totally stubby. From the standpoint of reducing LSA flooding this would probably be optimum.


You are the only person in this discussion that knows enough about your network environment to be able to choose which approach is the "optimum".


HTH


Rick

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