classless vs classful routing protocols

Every IP routing protocol is classfull. ie, RIP, IGRP, EIGRP, OSPF, RIP V2.
It's the ability to route class A, B and C addresses.
It's when you you get into classless routing that some protocols don't support.
Alot of information to explain it all, so <A HREF="http://encyclopedia.thefreedictionary.com/classful network" target="_new">here</A> is some light reading. 😉

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Classful routing protocols do not include the mask in routing updates. For example, a RIP router will only send the IP of the network so that 10.5.2.0/24 and 10.1.0.0/16 will only be advertised as the 10.0.0.0/8 network. Classless routing protocols such as OSPF will include the mask and be able to see that these are different networks.

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Class ful:
Classful routing Protocol does not send subnet mask info at what time a route update is send out. Each and every one device in the system has to make use of the similar subnet mask. Classfull routing does not allows Variable Length Subnet Masking.
For example : RIP V1 & IGRP

Class less:
Classless routing sends subnet mask info within the routing updates [at what time a route update is send out.]. Classless routing allows Variable Length Subnet Masking.
For example : RIP V2 EIGRP & OSPF.
2) Mulitcasting : Any statement between a single sender as well as many receivers.

http://ccnaanswers-khim.blogspot.com/2011/04/classful-and-classless-routing.html