Dynamic Routing

Dynamic routing performs the same function as static routing except it is more robust. Dynamic routing allows routing tables in routers to change as the possible routes change. Dynamic routing protocols do not change how routing is done. They just allow for dynamic altering of routing tables.
There are two classifications of protocols:

1.      IGP - Interior Gateway Protocol. The name used to describe the fact that each system on the internet can choose its own routing protocol. RIP and OSPF are interior gateway protocols.

2.      EGP - Exterior Gateway Protocol. Used between routers of different systems. There are two of these, the first having the same name as this protocol description:

1.      EGP - Exterior Gateway Protocol

2.      BGP - Border Gateway Protocol.

Dynamic routing protocols are software applications that dynamically discover network destinations and how to get to them. A router will ‘learn’ routes to all directly connected networks first. It will then learn routes from other routers that run the same routing protocol. The router will then sort through its list of routes and select one or more ‘best’ routes for each network destination it knows or has learned.

Dynamic protocols will then distribute this ‘best route’ information to other routers running the same routing protocol, thereby extending the information on what networks exist and can be reached. This gives dynamic routing protocols the ability to adapt to logical network topology changes, equipment failures or network outages ‘on the fly’.

Conceptually, the dynamic routing method has two parts: the routing protocol that is used between neighboring routers to convey information about their network environment, and the routing algorithm that determines paths through that network. The protocol defines the method used to share the information externally, whereas the algorithm is the method used to process the information internally.