Monday, 15 December 2008
I have been plugging away at a few mini labs from Narbik's Advanced Technology Workbooks. (whoops I think I was so busy that I forgot to mention that I bought these in November just before the pound plummeted to much.) The workbooks are really good (I promise once I am through them I will compare them with the Internetwork Expert and the IPExpert workbooks) although I am taking my time getting through them. I am using Dynamips to run the workbooks so I have a topology that seems to work for the moment. I am still going through the OSPF section so I have not made great progress but I am repeating several of the mini labs to see if I can understand them a bit better.
The plan is to try and finish the OSPF section before my Christmas holiday in a weeks time and then start up again in the new year. Also I hope to get some time to setup the IPExpert Dynamips topology for my different machines, and if I get any free time over Christmas the plan it to at least hit the CCIE Command Memorizer to ensure I retain a bit of knowledge over the festive season.
In case I do not get a chance to post again best wishes to you and your families where ever you are in the world over the holiday season.
Tuesday, 9 December 2008
OSPF uses Dijkstra's SPF algorithm to compute the shortest path tree (SPT). During the computation of the SPT, the shortest path to each node is discovered. The topology tree is used to populate the routing table with routes to IP networks. When changes to a Type-1 or Type-2 link-state advertisement (LSA) occur in an area, the entire SPT is recomputed. In many cases, the entire SPT need not be recomputed because most of the tree remains unchanged. Incremental SPF allows the system to recompute only the affected part of the tree. Recomputing only a portion of the tree rather than the entire tree results in faster OSPF convergence and saves CPU resources. Note that if the change to a Type-1 or Type-2 LSA occurs in the calculating router itself, then the full SPT is performed.
Incremental SPF is scheduled in the same way as the full SPF. Routers enabled with incremental SPF and routers not enabled with incremental SPF can function in the same internetwork.Looks like quite a useful command to remember, so I will be adding it to my configs in future.