ccna1 examen final b

ccna1 examen final b.When changes occur in the network, LSAs are sent as floods. when LSA updates are received, the local topology is updated accordingly based on themdatabase.Benefits of Link State ProtocolOne advantage of link-state protocols is that they use a hierarchical structure that helps limit the extent of LSA propagation. This reduces the likelihood of network changes affecting all routers. This is unlike distance vectoring protocols that use a flat topology. With distance vectoring protocols, a change in one part of the network will eventually affect all the routers in the network; with link-state protocols, this may not be the case, depending on the configuration of the routers. For example, OSPF uses areas to help limit the impact of a change; therefore, a change in one area may not affect other areas.Another advantage of link-state protocols is that they use multicasts to share routing information. Multicasts are sent to a group of devices, while broadcasts are sent to all devices; only the other routers running the link-state protocol process LSA packets. In addition, link-state routers send only incremental updates. Incremental updates refer to updates sent outbound when the network state changes. This is much better than the distance vectoring protocol practice of broadcasting updates one-by-one at regular intervals (typically every 30 or 60 seconds). Once all link-state routers are up and informed of the network topology, updates are typically sent out only when changes occur (which should not be too frequent). The advantage of this approach is that network bandwidth and resources are used more efficiently than distance vectoring protocols.A third advantage of link-state protocols over distance vectoring protocols is that classless routing is supported. Classless routing allows you to aggregate a large number of contiguous routes into a small number of routes, which is referred to as variable-length subnet masking (VLSM) and classless inter-domain routing (CIDR), concepts that are discussed in depth in Chapter 7.By aggregating routes, routing efficiency can be improved. First, fewer routes are advertised; second, aggregated routes fail only when all subnets and networks included in the aggregated route are down. For example, there may be a constantly flipped WAN link (a flipped route is one that constantly switches between normal and abnormal), which can cause serious performance problems for link-state protocols. With aggregation, even if the aggregated route contains a specific route that keeps flipping, it does not affect the state of the aggregated route, which in turn affects the many routers in the network. Third, by aggregating routes, the size of a router's link-state database can be reduced, which in turn reduces the CPU cycles required to run the SPF algorithm and to update the routing table, and reduces the amount of router memory occupied by the routing protocol.A fourth advantage of link-state protocols is that by using the SPF algorithm, routing loops do not appear in the routing table: by looking at the upside-down tree, it is easy to spot loops and thus not add them to the routing table. However, routing loops can pose a problem for distance vectoring protocols, which is discussed later in this chapter in the section "Problems with Distance Vectoring Protocols and Their Solutions".Disadvantages of Link State ProtocolsWhile link-state protocols have many advantages, they also have disadvantages. For example, while link-state protocols allow networks to scale to much larger sizes than distance-vector protocols, they also take up more CPU and memory. Link-state protocols must maintain more tables in memory: a neighbor table, a link-state database, and a routing table. When the network changes, the router must update the link-state database, run the