OSPF Stubby & Totally Stubby, explained

OSPF (Open Shortest Path First) has many configurable topologies. One of being the  Stubby Area,  as if that didn’t confuse you enough they introduced  the Totally Stubby Area when this was first explain to me, I couldn’t grasp the concept of what the instructor was talking about, at least not until I drew the network out and configured it out in GNS3, it was then I was able to seen it for myself.

FYI OSPF overview, stubby networks only used for a small area that need to block all the external routes in their routing table.   Routing will show a default internal route pointing to their ABR. Generally in the OSPF world all things must connect to Area 0, the ISP link would normally flow out Area 0 ASBR  I think of Area 0 as the OSPF body and other area as limbs (the analogy works for me). Click topology for larger pic.

router#router ospf 1
router#area 1 stub

You also need to do the same config on the corresponding ABR

All E2 routes should gone and you should see a summary internal candidate default route of O*IA [110/65] via

Totally stubby networks block type 3, 4, and 5  from entering their route table.  Side note, Totally stubby area is a Cisco Preparatory design, some vendors have adopted it.   **ADD250X250**

We move over to Area 2 and configure the ABR

router#router ospf 1
router#area 2 stub no-summary (this makes it a totally stubby area)

At this point your neighbor relation will fail until you configure the router in area 2

router#router ospf
router#area 2 stub (note no summary needed here)

Once completed you should only see one default route in your ospf routing table. O*IA [110/65] via

Here’s what we did

  1. Configured a Stubby network and kept the external routes (E2, which is the default route type) out of Area 1, and only allow the internal (IA) summarized routes to come through, IA.

  2. Configured a Totally Stubby network isolating it to Area 2  with just a default route to its neighbor

Stay tuned for Not So Stubby and Not So Totally Stubby

Updated : 2012-04-Cleaned up document formatting

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