routing with ospf

Unanswered Question
Sep 8th, 2010

Would you recommend running single area ospf on both the core and remote sites?

We're running rip at the moment and we want to migrate to ospf. We have about 20 routers, 250+ routes, and 10 remote sites.

Are there any document on how to migrate to different protocol?

Thanks

I have this problem too.
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Atif Awan Wed, 09/08/2010 - 08:27

It is best to start with a hierarchical design as opposed to a flat OSPF area. Usually the core runs Area 0 while branches are made part of different OSPF areas with an upper limit defined on how many branches to be provisioned per area. In your case since you have only 10 branches one additional area will suffice. You also need to look at summarization at the Area boundary but your IP Addressing should be contiguous in order to achieve this in an effective manner. You can also look at putting branches in a Stub or Totally Stub area to enhance scalability. I will strongly recommend you go through some collateral on OSPF first so that you understand the basics and how to scale the protocol. A network designed properly from the beginning will scale well and will keep the operational overhead under control.

Atif

after1111 Thu, 09/09/2010 - 09:20

Hi Atif,

Thanks for the advice.

Practically, how many ospf areas should be use in a Production network?

Would you recommend a distribution layer device to perform ABR or should I use a separate router for ABR?

Atif Awan Thu, 09/09/2010 - 09:32

Practically, how many ospf areas should be use in a Production network?

There is no definitive answer to this. It depends on the size of the network and to its regional hierarchy. Usual points discussed during such a design are around the total number of routers per OSPF Area as well as the total number of Areas per ABR. If you have a small network I guess you need Area 0 for backbone and one Area per region for branches.

Would you recommend a distribution layer device to perform ABR or should I use a separate router for ABR?

Again it depends on the size of the network. Most large networks have dedicated routers performing branch aggregation and acting as ABRs for a particular set of branches. If the size of the network does not warrant this you can have the distribution routers serve as branch aggregators and these will automatically be ABRs. The usual practice is to avoid the core routers being ABRs.

Atif

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