Routing can be defined as the process of paths selection along which the traffic has to be sent in a network. Routing concept holds good for different kinds of network such as the following:
– Telephone networks or circuit switching networks
– Electronic data networks or internet
– Transportation networks
Here we focus on routing in the second type of networks using the packet switching technology.
Routing in networks that use packet switching technology
– In these networks the packet forwarding is directed by the routing.
– The transition of the logically addressed packets takes place from their source to the final destination via the intermediate nodes.
– These nodes are nothing but typical hardware devices such as bridges, routers, firewalls, switches and gateways.
– Forwarding packets and routing can be performed by a general purpose computer system even though if it does not possess specialized hardware for this purpose.
– But the performance would of course be limited.
– Routing tables are used by a routing process to direct the packet forwarding process and maintenance of the record of routes that link to various destinations.
– This is why the construction of routing table is important to carry out efficient routing and these tables are stored in the memory of the router.
– Mostly, only one network path is used by the routing algorithms at a time.
– But in some cases multiple alternative paths are required.
– This requirement is fulfilled by the multi-path routing techniques.
– There are many routing schemes that differ based up on their delivery semantics:
1. Unicast: The message is delivered to a specified single node.
2. Broadcast: The message is delivered to all the nodes of the network.
3. Multicast: The message is delivered to only groups of nodes that hold an interest in receiving the message.
4. Anycast: The message is delivered to any one node out of a group usually the one whichlies nearest to the source.
5. Geocast: The message is delivered to the geographic area.
About Unicast Scheme
– Out of all these, the most widely used is the unicast scheme.
– Static routing is all based up on the manual configuration of the routing tables.
– But this is only in the case when the network size is small.
– In other cases where the networks are quite large, complex topologies are followed.
– The characteristic feature of these topologies is that they change frequently thus proving to be a hindrance in the manual construction of the routing table.
– Below we state some unicast algorithms:
1. Distance vector algorithms
2. Link state algorithms
3. Optimized link state routing algorithm
4. Path vector protocol
More about Routing in Networking
– In path selection, a routing metric is applied to multiple routes so as to select the best route.
– This metric is obtained via a routing algorithm and might cover information about the network delay, hop count, bandwidth, MTU, communication cost, path cost, load and so on.
– The best possible paths are then stored in the routing table and all other information might be stored by the topological databases.
– The routing is specific for every routing protocol.
– Some external heuristic is to be used by the multi – protocol routers for the selection of routes from among the ones learnt from protocols.
– In some cases, host specific routes might be set up by the local network administrator for a particular machine.
– Thus, the network usage remains in more control permitting security and testing.
– Such routes are helpful whenever debugging of the network connections is required.
– In some cases, multiple entities are involved in the path selection which makes the routing more complicated.
– Things can further get complicated if each of these entities tries to optimize the path as per its objectives.
– ISPs or the internet service providers are the autonomous systems in to which the internet is divided.
– These systems only control the routes of their networks at various levels.
– Route analytics tools as well as techniques are used for monitoring the routing posture of the networks.