Exam Essentials

Understand the operation of OSPF. OSPF areas are defined by the network designer and established using the multicast Hello protocol, which includes such things as the router ID, timing intervals, existing neighbors, area identification, and so on. Adjacency tables are built, and the DR and BDR are chosen before link-state information is updated and exchanged. LSAs are used to designate the types of updates, and router types are used to control the exchange of route tables.

Know the configuration of OSPF. OSPF internal, ABR, and ASBR routers require different configuration. All routers must be configured with a process ID and an area ID. During the router ospf process-id configuration, wildcard masks are used along with network statements for the networks and areas to advertise. Route summarization is configured on the ABR for inter-area routing, and external summarization is configured on the ASBR.

Remember the use of NLSP. NLSP can be used by Novell servers or Cisco routers to exchange and maintain a link-state database or route table of IPX network routes. The three databases are adjacency, link-state, and forwarding. The link-state database is derived from the adjacency database, which maintains neighbor relationships, and the forwarding database, also known as the route table, is built.

Understand the operation of IS-IS. Larger IS-IS networks are organized into a backbone area made up of the connected set of all Level 2 routers from all areas, which in turn is connected to local areas. Between areas, routers know how to reach the backbone, and the backbone routers know how to reach other areas. Routers establish Level 1 adjacencies to perform routing within a local area (intra-area routing). Routers establish Level 2 adjacencies to perform routing between Level 1 areas.

Know how to configure IS-IS. You must configure the parameters for each instance of the IS-IS routing process individually. Network entity titles (NETs) define the area addresses for the IS-IS area and the system ID of the router. To enable IS-IS and specify the area for each instance of the IS-IS routing process, the following commands in global configuration mode are used:

• router

• isis [area tag]

• net network-entity-title

Understand the use and operation of bridging protocols. Transparent bridging doesn’t modify, address, or receive frames but is responsible for listening, learning, filtering, and forwarding of packets. Loop avoidance is also dealt with at the OSI Layer 2 with the Spanning-Tree Protocol. STP finds the loops between bridges and switches at Layer 2 and elects a root bridge, which is then used by all other bridges and switches to calculate the shortest path to the root bridge and disable any ports that create a loop.