As you read this section, consider the following questions: What is static routing? What are its advantages and disadvantages?
The simplest solution is to pre-compute all the routing tables of all routers and to install them on each router. Several algorithms can be used to compute these tables.
A simple solution is to use shortest path routing and to minimise the number of intermediate routers to reach each destination. More complex algorithms can take into account the expected load on the links to ensure that congestion does not occur for a given traffic demand. These algorithms must all ensure that:
- all routers are configured with a route to reach each destination
- none of the paths composed with the entries found in the routing tables contain a cycle. Such a cycle would lead to a forwarding loop.
The figure below shows sample routing tables in a five routers network.
Figure 5.8: Routing tables in a simple network
The main drawback of static routing is that it does not adapt to the evolution of the network. When a new router or link is added, all routing tables must be recomputed. Furthermore, when a link or router fails, the routing tables must be updated as well.
Source: Olivier Bonaventure, https://s3.amazonaws.com/saylordotorg-resources/wwwresources/site/wp-content/uploads/2012/02/Computer-Networking-Principles-Bonaventure-1-30-31-OTC1.pdf
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