What is one reason link-state protocols are more efficient than distance-vector algorithms?
3.
Which parameter of the route command clears all existing routing table entries?
4.
What ID is reserved for the OSPF backbone?
5.
What is one of the major problems with distance-vector routing?
Answers to Review Questions
1.
A topological database is essentially an overall picture of networks in relationship to routers. A topological database contains the collection of LSAs received from all routers in the same area. In a very large AS with a large number of networks, each OSPF router must keep the LSA of every other router in its topological database. Each router in a large OSPF AS has a large topological database. The SPF calculation of a large topological database can require a substantial amount of processing and can result in very large routing tables. To prevent this, ASs are divided into areas. For more information, see the section "Working with OSPF."
2.
A link-state routing protocol is generally more efficient than a distance-vector protocol. The fact that LSAs contain only information about the neighbors of a particular router leads to smaller routing tables. For large networks, the LSAs contain only neighbor information, and therefore the impact on the network is much less than it would be on a network using a distance-vector routing protocol. With a distance-vector routing protocol, all the routes in a routing table are propagated, resulting in more usage of bandwidth than link-state protocols. In addition, because link-state information is not exchanged after the network has converged, it does not have the impact on the network that distance-vector routing does. By default, distance-vector routing broadcasts its information on a periodic basis, whether the information is required or not. For more information, see the section "Routing Protocols."
3.
The -f parameter is used to clear the routing tables of all entries. For more information, see the section "Using the route Command to Configure Static Routes."
4.
An OSPF backbone has a reserved area ID of 0.0.0.0. An OSPF backbone is responsible for distributing routing information between areas. There is at least one backbone per OSPF internetwork. It consists of all area border routers, networks that are not in any one area, and their attached routers. The backbone has to be at the center of all areas within the AS. That is, all areas have to be physically connected to the backbone. This is because OSPF expects all areas to inject routing information into the backbone, and in turn the backbone will disseminate that information into other areas. For more information, see the section "Working with OSPF."
5.
The count-to-infinity problem is one of the major disadvantages of distance-vector routing. This condition is caused when a router (or a link to a router) becomes unavailable. The convergence time is slow and, therefore, incorrect routing information is propagated through the system. For more information, see the section "Routing Protocols."
