Classful and classless routing protocols
All routing protocols can also be classified-
1. Classful routing protocols
These protocols do not send subnet mask information in their routing updates.Teh first routing protocol RIP is classful protocol. It was introduced when network addresses were allocated based on classes-classA,classB and class C.RIP need not to include the subnet mask in the routing updates because the network mask could be determined based on the first octet on the network address.Classful routing protocols cannot be used when a network is subnetted using more than one subnet mask. In the other word we can say it does not support the Variable length subnet mask (VLSM).classful routing protocols are RIPv1 and IGRP.
2. Classless routing protocols
These protocols include the subnet mask with the network address in routing updates. Classless routing protocols are required in most network today because they support VLSM, discontiguous network etc.Classless routing protocols are RIPv2, EIGRP, OSPF, IS-IS and BGP.
Convergence
This is the important characteristic of a routing protocols that determine how quickly it converges when there is change in the topology.Teh network has converged networked when all the router have complete and the accurate information ,calculate the best path for the destination, and updates their routing tables. A network is not completely work until it has converged. The router share information each router but independently calculate the effect of topology changes on their routes. Routing protocol can be rated based on the speed to convergence, it means the faster the convergence the better the routing protocol. RIP and IGRP are slow to converge while EIGRP, OSPF, IS-IS are faster to converge.
When routing protocols information is enable, a router attempt to exchange the information about the topology of the network. A state of convergence achieve when all the link information is propagated in the entire router .Any changes in the network that effect routing table will break the convergence until this change has been successfully communicated to all others routers. Converge time measure how fast a group of router reaches the convergence state. Routing protocol RIP converge very slow, even a networks of few routers can take a minute or two while the OSPF is fast converging protocol. A network of few routers converge in seconds using OSPF.
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