Plannong Lecture 8:Network Routing Protocols

Planning for Information Network
Lecture 8:Network Routing Protocols

Routing protocol features
There are many ways to characterize routing protocols, including the following:
? Static versus dynamic routing
? Interior versus exterior routing protocols
? Distance vector versus link-state versus hybrid protocols
? Routing protocol metrics
? Routing protocol convergence
? Flat versus hierarchical routing protocols

Static Routing
The term static routing denotes the use of manually configured or injected static routes for traffic forwarding purposes. Using a static route might be appropriate in the following circumstances:
? When it is undesirable to have dynamic routing updates forwarded across slow bandwidth links, such as a dialup link.
? When the administrator needs total control over the routes used by the router.
? When it is necessary to reach a network that is accessible by only one path (a stub network)
A stub network is a computer network, or part of an internetwork, with no knowledge of other networks, that will typically send much or all of its non-local traffic out via a single path, with the network aware only of a default route to non-local destinations.
* Configuring and maintaining static routes is time-consuming.
* Properly implementing static routes requires complete knowledge of the entire network.
Static routes are unidirectional. A static route configured in one direction via one router must have a corresponding static route configured on the adjacent router, in the opposite direction, for the return path.
Static routes are appropriate in situations such as with stub networks, hub-and-spoke connections (Star connections), and dialup environments.

Dynamic Routing
Dynamic routing allows the network to adjust to changes in the topology automatically, without administrator involvement.
A static route cannot dynamically respond to changes in the network. If a link fails, the static route is no longer valid if it is configured to use that failed link, so a new static route must be configured. If a new router or new link is added, that information must also be configured on every router in the network. In a very large or unstable network, these changes can lead to considerable work for network administrators. It can also take a long time for every router in the network to receive the correct information. In situations such as these, it might be better to have the routers receive information about networks and links from each other using a dynamic routing protocol.