DYNAMIC ROUTING

Routing protocols are used to enable the routers exchange routing information, they allow routers to learn about remotely connected networks dynamically. This information is then added to their routing tables as a basis for forwarding packets.Now that we have an overview of routing protocols, we need to understand how they work.

Routing protocols are comprised of processes, messages and algorithms that are used by routers to learn about remotely connected networks from routers that have been configured with the same routing protocols, the routes that have been learnt are added to the routing table and used as a basis for forwarding packets.

• Routing protocols function by:
• Discovering remote networks
• Maintaining current routing information
• Path determination

The routing protocol is made up of these components.

1. Data structures – this is information about remote networks. It is usually stored in the RAM and may be comprised of tables such as neighbor tables and topology tables.
2. Algorithm – this is the sequential list of steps that the routing takes when determining the best path to a particular network.
3. Routing protocol messages – these are messages that are used to maintain updated routing information. Examples include; hello messages, update messages among others.

The way routing protocols operate may differ depending on the routing protocol, however, there are certain characteristics inherent in every routing protocol.

• Exchange of information on interfaces to discover neighboring routers
• Exchange of routes that have been advertised
• Running of the algorithm so as to determine the best path
• Adding of best paths to the routing table
• Detection of topology changes and making the necessary changes

These are the general steps routers will take. However, the processes differ with each routing protocol and will be discussed at a later stage

Distance vector means that routes are advertised as vectors of distance and direction. If we take an example of a tourist getting directions, distance vector protocols would be where the tourist would only use road signs to get to where they are going. They do not know the exact landscape and possible blocks, they only know of the next point towards their destination.

Distance vector protocols work best in situations where:

• The network is simple and flat and does not require a special hierarchical design.
• The administrators do not have enough knowledge to configure and troubleshoot link-state protocols.
• Specific types of networks, such as hub-and-spoke networks, are being implemented.
• Worst-case convergence times in a network are not a concern

On the other hand, if the tourist had an entire map of the desired destination, with details of different paths to where they were going, they would be using a link-state routing protocol.

Link state routing protocols usually have a complete view of the topology. They usually know of the best paths as well as backup paths to networks. Link state protocols use the shortest-path first algorithm to find the best path to a network.