OSPF Features

3.4 You are concerned about the convergence times and CPU resources consumed in the backbone OPSF area. Configure all routers in the backbone so that they only recalculate a portion of the Shortest Path Tree when they receive local link state advertisements.
2 points


This one would have thrown me during my exam! It is one of those “I did not know a router could do that” moments. I skip this 2 point, non-core task until the end of the core configurations and easier non-core tasks.

Once I am ready to research and tackle this task, I do not recall that this feature is  documented in the “standard configuration guide” area for OSPF. So my first area of research will be the new features documentation.

I start at the new DOC-CD Home Page and use the following navigation:
Cisco IOS -> Release 12.4 Family -> 12.4 Mainline -> General Information -> Release Notes -> Part 3: New Feature Descriptions and Important Notes

I quickly scan the OSPF new features – and it sounds like I might have a winner - OSPF Incremental SPF.  Checking that article quickly, I realize I have found the correct feature. On all backbone routers I configure the following:

router ospf 1

Certainly a painless configuration. The only real gotcha would be ensuring you do not accidentally miss a backbone device.

NOTE: One of our blog readers (Mike), pointed out for us that this feature is now documented in the “standard configuration guide” area for OSPF. It is a subsection under the main configuration area, so this would be even more direct to find than New Features. Awesome.

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