Classless Routing/Classful Routing

typesh

Hey everyone,

I had a question about Classfull and Classless routing. I was reading something today that said CIDR allows routing decisions to be made based on the IP Address (network number) and Subnetmask, and that whether the IP Address is a Class A, B, or C makes no difference.

My question is, when does the Class of an IP make a difference regarding Routing Decisions?

Thank you.

citinerd

The classful routing assumes the classful subnet, so if we are dealing with a class B address it assumes the subnet 255.255.0.0 (there are some exceptions with subnetting). The Classless routing protocols includes subnets in the routing table updates. This allows for VLSM.

typesh

citinerd wrote: »

The classful routing assumes the classful subnet, so if we are dealing with a class B address it assumes the subnet 255.255.0.0 (there are some exceptions with subnetting). The Classless routing protocols includes subnets in the routing table updates. This allows for VLSM.

Hey thanks!

daveccna

Speaking of VLSM, can anyone direct me to an artical (or better yet explain) what considerations there are in implementing this in a real network. IE pre requisits, physical and otherwise.

mattrgee

daveccna wrote: »

Speaking of VLSM, can anyone direct me to an artical (or better yet explain) what considerations there are in implementing this in a real network. IE pre requisits, physical and otherwise.

How many hosts do you need to support and how many subnets to do you need? Are the first questions you should ask.

daveccna

mattrgee wrote: »

How many hosts do you need to support and how many subnets to do you need? Are the first questions you should ask.

I ask these questions in normal subnetting. I've read that VLSM is good for producing subnets of varying sizes but produces hirearchical logical networks as a consequence. See supernetting. I guess there's nothing for it but for me to hit the texts.

<Flagellates self> Bad dave! Dont be lazy!