IGP

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

SOLUTION:

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
ispf

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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