Classful vs Classless Routing Protocol
Classful Routing Protocol
1.Classful routing protocols' mask are same. i.e. All subnet masks must be the same on all
devices in the network.
2.Classful routing protocols do not transmit the subnet mask information along with the subnet
number.
3.Classful routing protocols do not allow VLSM, summarization, and discontiguous networks.
i.e.Classful routing does not allow subnetworks.
4.RIPv1 and IGRP are Classful routing protocols and supports only full length subnet
mask(default network with default mask).
If you are using a classful routing protocol, you cannot change the subnet mask. You
have to use the default subnet mask. For example, if you have a Class A network
address of 10.0.0.0/8 with subnets 10.0.10.0, 10.0.20.0, and 10.0.30.0., you would
only type in the classful network address of 10.0.0.0 and let RIP find the subnets and
place them in the routing table. In this case the default subnet mask is a /8 or
255.0.0.0.
Classless Routing Protocol
1.Routing protocols that supports VLSM which send mask information along with the routing
information are calledClassless routing protocols.
i.e.The use of Variable Length Subnet Mask(VLSM) is permitted inClassless routing protocols.
2.Classless routing protocols allow VLSM(Can have discontiguous subnets, better IP
addressing allocation), CIDR(More control over route summarization), and discontiguous
networks.
3.Classless routing protocols’ have the ability to carry subnet masks in their route
advertisements. i.e. Classless routing protocols do transmit subnet mask information.
4.Subnet mask and 32-bit address informations are contained in the routing updates of Classless
routing protocols.
5.RIPv2, EIGRP, OSPF, IS-IS and BGPv4 are all Classless routing protocols.
If you are using a classless routing protocol you can change the subnet mask. You need
not to use the default subnet mask. For example, if you have a 192.168.X.X network,
the default subnet mask is a /24 or 255.255.255.0. You can use subnet mask /25 or /26
or /27 etc.
http://aspell.org/CCNA/CCNA-Cisco-Classful-vs-Classless-Routing-Protocol.php