Routing cost, or a value assigned to a particular route as judged by the network administrator; the more desirable the path, the lower its cost•Reliability of a potential path, based on historical performance•The topology of a network38. OSPF (Open Shortest Path First) is an IGP and a link-state routing protocol used on interior or border routers. It was introduced as an improvement to RIP and can coexist with RIP (or RIPv2) on a network. Unlike RIP, OSPF imposes no hop limits on a transmission path. Also, OSPF uses a more complex algorithm for determining best paths than what RIP uses. Under optimal network conditions, the best path is the most direct path between two points. If excessive traffic levels or an outage preclude data from following the most direct path, a router may determine that the most efficient path actually goes through additional routers. Each
Chapter3Page 8 router running OSPF maintains a database of the other routers’ links. If OSPF learns of the failure of a given link, the router can rapidly compute an alternate path. This calculation demands more memory and CPU power than RIP would, but it keeps network bandwidth to a minimum and provides a very fast convergence time, often invisible to users. The algorithms used by link-state protocols and their faster convergence time also prevent routing loops. OSPF is supported by all modern routers. Therefore, it is commonly used on autonomous systems that rely on a mix of routers from different manufacturers.39. Static routing is a technique in which a network administrator configures a routing table to direct messages along specific paths between networks. Static routes are appropriate in certain situations, such as the static route between a small business and its ISP. However, static routes used to traverse several networks don’t account for occasional network congestion, failed connections, or device moves, and they require human intervention. Dynamic routing, on the other hand, automatically calculates the best path between two networks and accumulates this information in the routing table. If congestion or failures affect the network, a router using dynamic routing can detect the problems and reroute messages through a different path. By default, when a router is added to a network, dynamic routing ensures that the new router’s routing tables are updated.40. An ARP table can contain two types of entries: dynamic and static. Dynamic ARP table entries are created when a client makes an ARP request that could not be satisfied by data already in the ARP table. Static ARP table entries are those that someone has entered manually using the ARP utility.
- Fall '14
- Router, Transmission Control Protocol, routing protocol