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New Member

Stopping OSPF E2 Routes at an ABR

Can static routes being redistributed into ospf (via redistribute static subnets) be stopped at the ABR from going from area 0 to another area? Can they be stopped at the ABR from going from, say area 1 to area 0? Need a relatively clean way of keeping some external routes local to a single ospf area that requires as little configuration effort as possible.

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Bronze

Re: Stopping OSPF E2 Routes at an ABR

To keep external routes from entering an area from area 0, that area must be configured as either a stub area, which has no external routes, or a not-so-stubby area (NSSA), which allows type 7 external LSAs. The default behavior for a NSSA ABR is to convert these type 7 LSAs into type 5 ("normal" external) LSAs and send them into area 0.

The only way to block external LSAs from an area to area 0 is to configure that area as a NSSA, and in the ABR(s) for the area enter the command "summary address (prefix) (mask) not advertise" in the OSPF configuration mode.

Hope this helps.

Mark

New Member

Re: Stopping OSPF E2 Routes at an ABR

Mark

Thanks for your reply. We are currently using nssa areas, this problem is one reason why. However, this arose in an existing area with over forty routers and redefining all of them as nssa seems too big a hammer for this problem - the static routes are only affecting about six. Was trying to avoid reconfiguring these six, hoping that only the two ABRs could be "fixed".

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