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TOPIC: OSPF and Default Routes

OSPF and Default Routes 10 years 6 months ago #13739

  • jwj
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A network I'm working on is planning on changing from static routes to a single OSPF area (area 0). I'd like to keep the default routes to the internet provider the same.

e.g. ip route 0.0.0.0 0.0.0.0 Serial1/1

What do I need to do to make a default route work with OSPF? Do I just need to add the line "default-information originate" to the OSPF configuration? The serial interfaces all have an IP address with a /30 mask, do those networks need to be added to the OSPF config as well?

Thanks in advance.
-Jeremy-
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Re: OSPF and Default Routes 10 years 6 months ago #13743

  • reaper
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Default-information originate should do the trick. You don't need to advertise directly connected networks but I don't think you will screw anything up doing so either :D
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Re: OSPF and Default Routes 10 years 6 months ago #13744

  • havohej
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I understand all routers are directly connected by the serial interfaces??
so the answer is yes, in each router directly connected to area 0 you must setup /30 wan network, and /24 (or whatever /you have in the lan) to belong to the same area 0.
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Re: OSPF and Default Routes 10 years 6 months ago #13747

  • jwj
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Sorry, I meant that the internet provider is connected via the serials (right now 2 T-1's that are using CEF load balancing) and the internal network (consisting of a few more routers) is connected via the ethernet interfaces. So I can just leave the default routes for the serial interfaces, and it will work just fine with the OSPF configuration for the rest of the network?
-Jeremy-
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Re: OSPF and Default Routes 10 years 6 months ago #13758

  • havohej
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Hi.

so you are only using a single area for all ospf routers, and only one router redistributing the default route within the area to all the routers.

It will work ok, and the topology you are using is a NSSA, the router redistributing the default route acts as ASBR.

It will work ok, but if the network is growing or plans to grow, or you want to create another area, for segmenting, the default route originated in the original area, by default does not propagate to the new created area, unless configuration intervention.
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Re: OSPF and Default Routes 10 years 6 months ago #13759

  • jwj
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Ok, this all makes sense after I made a small mock-up with some test 2600 routers. So if I added another area, what would I need to do, just add network 0.0.0.0 255.255.255.255 to area 0 for the new area's routers?
-Jeremy-
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