Welcome to CCNP Tutorials. The objective of these tutorials is to provide in depth understand of CCNP.
In addition to free CCNP Tutorials, we will cover common interview questions, issues and how to’s of CCNP.
The collection of all the link-states would form a link-state database.
The first thing that happens is that each node, router, on the network announces its own piece of link-state information to other all other routers on the network. This includes who their neighboring routers are and the cost of the link between them.
Each router sends these announcements to all of the routers in the network.
Each router collects all of this link-state information from other routers and puts it into a topological database.
Using this information, the routers can recreate a topology graph of the network.
Believe it or not, this is actually a very simple algorithm and we highly suggest you look at it some time, or even better, take a class on algorithms. (Radia Perlman’s book, Interconnections, has a very nice example of how to build this graph – she is one of the contributors to the SPF and Spanning-Tree algorithms.
This algorithm creates an SPF tree, with the router making itself the root of the tree and the other routers and links to those routers, the various branches.
Using this information, the router creates a routing table.
-Process-id is locally significant, and does not have to be the same number on other routers (they don’t care).
-This is different than the process-id used for IGRP and EIGRP which must be the same on all routers sharing routing information.
-Extra: FYI - Cisco IOS limits the number of dynamic routing processes to 30. This is because it limits the number of protocol descriptors to 32, using one for connected route sources, one for static route sources, and 30 for dynamic route sources.
-Tells OSPF which interfaces to enable OSPF on (send and receive updates), matching the address and wildcard mask.
-Most of the time you can just use an inverse-mask (like access-lists) as the network wildcard mask.
-Very useful in setting Router IDs as they never go down.
-Extra: Also, useful to configure “virtual” networks that you can ping and route as if they were attached networks.
-Router with the highest Router ID is elected the DR, next is BDR.
-But like other elections, this one can be rigged.
-Changes the default bandwidth metric on a specific interface.
-Used in the 108/bandwidth calculation for cumulating the cost of a route from the router to the network on the outgoing interfaces.
-Does not modify the actual speed of the link.
-Common for multi-vendor environments.