Module 6: Summary

Module 6: Summary

This page summarizes the topics discussed in this module.
The process that a router uses to forward packets toward the destination network is called routing. Decisions are based upon the destination IP address of each packet. When routers use dynamic routing, they learn about remote networks from other routers. When static routing is used, a network administrator configures information about remote networks manually.
Static route operations can be divided into these three parts. First a network administrator uses the ip route command to configure a static route. Then the router installs the route in the routing table. Finally, the route is used to route packets.
Static routes can be used for backup purposes. A static route can be configured on a router that will only be used when the dynamically learned route has failed.
After static routes are configured, verify they are present in the routing table and that routing works as expected. Use the command show running-config to view the active configuration in RAM. The show ip route command is used to make sure that the static route is present in the routing table.
The communication used between routers is referred to as a routing protocol. The goal of a routing protocol is to build and maintain the routing table.
A routed protocol is used to direct user traffic. A routed protocol provides enough information in its network layer address to allow a packet to be forwarded from one host to another based on the addressing scheme.
An AS is a collection of networks under the same administration that share a common routing strategy. Autonomous systems divide the global internetwork into smaller and more manageable networks. Each AS has its own set of rules and policies and a number that distinguishes it from all other autonomous systems.
The distance vector routing approach determines the direction, or vector, and distance to any link in an internetwork. The link-state approach recreates the exact topology of an entire internetwork.
Distance vector routing algorithms pass periodic copies of a routing table from router to router. These regular updates between routers communicate topology changes. The distance vector routing algorithm is also known as the Bellman-Ford algorithm.
The second basic algorithm used for routing is the link-state algorithm. The link-state algorithm is also known as the Dijkstra algorithm or as the SPF algorithm. Link-state routing algorithms maintain a complex database of topology information. The distance vector algorithm has nonspecific information about distant networks and no knowledge of distant routers. A link-state routing algorithm maintains full knowledge of distant routers and how they interconnect.
Interior routing protocols are designed for use in a network whose parts are under the control of a single organization. An exterior routing protocol is designed for use between two different networks that are under the control of two different organizations. These are typically used between ISPs or between a company and an ISP.