Clasful / Classless network definition

agustinchernitsky

Hi Everyone,

I am reading Todd Lammle Sybex CCNA book, and I have one doubt: Whats the correct classful and classless network definition??

Acording (or what I understood) from the book a classful network is a network that uses the same subnet everywhere, while classless use different subnets (ie using VLMS).

Is this correct?

gracias amigos!

bighornsheep

A classful network will only use 255 or 0 in the subnet octet but 0 must be the last octet, so 255.0.255.0 is not a valid subnet mask. This will allocate a set number of hosts to every subnet, and VLAN is the (I think the only) way to seperate broadcast domains.

A classless network is basically a flexible form of the above, and you can use the custom subnet masks to specify subnets and number of hosts in them.

Webmaster

At the following page in the section Classless and Classful Routing Protocols is a RIPv1 example that explains it rather well www.ciscopress.com/articles/article.asp?p=330807&seqNum=4&rl=1
If a router in classful routing cannot determine the subnetmask based on its own interface, that would have to be in the same major network, it assumes either a class A, B, or C mask based on the IP address. In classless routing the network boundary can be at any bit, so classless routing protocols include the subnetmask. It basically ignores the original addressing schema with A, B, and C classes to allow more efficient use of the available address space.

HELLZxPHADER

10.40.40.1 /24
172.16.6.1 /32

classless routing protocols can advertise the above networks like this
10.40.40.0
172.16.6.1

classful routing protocols can only advertise the above networks like this
10.0.0.0
172.16.0.0

agustinchernitsky

Thanks everyone!