OSPF Configuration Approach

[Mokhalil82]

Hi 

Up till now I have configured OSPF in labbed environments using routers, now when trying to plan it in a production environment, questions I didn't think of previously come to mind. So I have a network with static routes where I want to implement ospf. My plan is to leave the statics in place and setup ospf and ensure routes are being learned correctly.

What is the best approach in deciding what networks to advertise etc. Would i go by looking at the existing routing table on each L3 switch (shows the connected and static routes) and advertising my connected routes using the network statements, and then redistributing the static routes into ospf.

Would this be a good approach or does anyone have anything better.

Thanks

[Jon Marshall · Accepted solution]

You advertise all networks you need to be reachable.

So usually you would have network statements under OSPF for your directly connected interfaces and then redistribute the statics as per your last post.

Your network statements can either be specific per interface or more general but that's a preference thing more than anything and you usually get more specific if you are trying to exclude certain networks from being advertised which you may not want.

Bear in mind if the statics are in place then you won't see the OSPF routes in the IP routing table for the same networks and you will have to check the OSPF database to see which LSAs the L3 device has received.

So configure OSPF on the devices and make sure the L3 devices are seeing each other as OSPF neighbors.

If you are unsure or not comfortable with checking the OSPF database then although I haven't done this before a failsafe may be to -

1) configure static routes which are a copy of what you have now but give them an AD > 110 (OSPF).

These won't be placed into the routing table because of the existing static routes.

2) when the OSPF neighborships are established and "sh ip ospf database" shows entries then you can remove the existing static routes.

3) if you missed an OSPF route then the temporary static with an AD > 110 would then be used which would show you that you needed to modify your OSPF configuration.

You may decide the above is too complicated but it would mean if you did miss some of the OSPF configuration you should not lose connectivity while you sorted it out.

Jon

[Mokhalil82]

Thanks Jon, i like the fail safe, didn't think of that. I know how to go about configuring ospf but as its my first time trying to configure it on a live network, Im trying to be sure ive covered all angles. 

Thanks again