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On the core router I use OSPF with other routers for internal networks and a default route to the ISP's router for Internet access. All internal routers have the CORE router as the default gateway.

In case that the connection to any of the internal routers/networks are not available I want the core router not to use the default route to look for any of the internal networks.

How?

6

In case that the connection to any of the internal routers/networks are not available I want the core router not to use the default route to look for any of the internal networks.

Configure a null0 route in your IGP core which covers all the IGP address space, then redistribute into area 0.

Example:

  ip route 10.0.0.0 255.0.0.0 null0

Now redistribute into ospf... You can optionally add a high admin distance if your routing policy requires it.

Example:

  router ospf 100
      redistribute static subnets
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  • I have to do this for every classfull internal networks? In other words 10, 172 and 192, three static routes in total. – 3D1L Dec 10 '14 at 16:58
  • That's close, more accurately "do this for every contiguous block of subnets in your internal network" – Mike Pennington Dec 10 '14 at 17:00

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