Classless & Classfull

up2thetime

Hello all

I needed some help distinguishing between classfull and classless terms.

For anyone with Odom's Second Edition, I am looking at Page 113.

Classfull means we are not subnetting, while classless means we subnet a Class A, B, or C address?

The world Clasless is throwing me off as it seems to imply the meaning "no class"

ncsugrad2002

up2thetime wrote: »

Hello all

I needed some help distinguishing between classfull and classless terms.

For anyone with Odom's Second Edition, I am looking at Page 113.

Classfull means we are not subnetting, while classless means we subnet a Class A, B, or C address?

The world Clasless is throwing me off as it seems to imply the meaning "no class"

on classless subnetting you can use different subnet masks for each section of the network. this conserves IP's as you don't have to use the same mask for each section.

on classful subnetting you have to use the same subnet mask on each portion of the network. i can give examples if you'd like.

also, some of the older routing protocols require you use classful subnetting. most of the newer ones are classless.

up2thetime

ncsugrad2002 wrote: »

on classless subnetting you can use different subnet masks for each section of the network. this conserves IP's as you don't have to use the same mask for each section.

on classful subnetting you have to use the same subnet mask on each portion of the network. i can give examples if you'd like.

also, some of the older routing protocols require you use classful subnetting. most of the newer ones are classless.

Hey thanks for responding.

Some examples would be great....

PC509

I think it means that with classless, you can run P2P links using a /30 and whatever else on a /26 or whatever you need to. Different subnet masks for different parts of the network. That way, you are using 2 hosts on 1 subnet for a P2P link, so you aren't wasting 252 addresses using a /24 mask. You would only need 2 for that link, no more. It would be a total waste to not go classless.

Classful is that you would have to use the /24 (or whatever) throughout your network for proper routing. Even on the P2P links. It would be very wasteful in some situations, although in others it may be useful.

I'm not a CCNA yet, but that is what I've been getting from studying so far. So, if I'm wrong, PLEASE correct me. You can elaborate as much as possible, too. I'd appreciate it!

ncsugrad2002

up2thetime wrote: »

Hey thanks for responding.

Some examples would be great....

K, I'd have to do some drawings for a visual

but basically if you have a situation where let's say you're given the range 192.168.10.0 through 192.168.0.255

In this example you're going to break that up into 3 subnets.

Subnet 1 needs 6 hosts
Subnet 2 needs 29 hosts
Subnet 3 needs 125 hosts

With classful addressing you have to use the same subnet mask for each of those ranges..and since the biggest subnet needs at least 125 hosts, you have to make your subnet mask 255.255.255.128. This results in a situation where you CAN'T make 3 networks (subnets) due to wasting so many addresses. If you tried to use that mask you'd get:

network 1: 192.168.0-127
network 2: 192.168.128-255
network 3: can't do it..out of addresses

Now, if you were able to use classless subnetting you can make the subnet masks different for each section of the network. So

you'd do it like

subnet 3 192.168.0.0-127 /25
subnet 2 192.168.0.128-159 /27
subnet 1 192.168.0.160-168 /29

now you've addressed all 3 networks and have plenty left

up2thetime

ncsugrad2002 wrote: »

K, I'd have to do some drawings for a visual

but basically if you have a situation where let's say you're given the range 192.168.10.0 through 192.168.0.255

In this example you're going to break that up into 3 subnets.

Subnet 1 needs 6 hosts
Subnet 2 needs 29 hosts
Subnet 3 needs 125 hosts

With classful addressing you have to use the same subnet mask for each of those ranges..and since the biggest subnet needs at least 125 hosts, you have to make your subnet mask 255.255.255.128. This results in a situation where you CAN'T make 3 networks (subnets) due to wasting so many addresses. If you tried to use that mask you'd get:

network 1: 192.168.0-127
network 2: 192.168.128-255
network 3: can't do it..out of addresses

Now, if you were able to use classless subnetting you can make the subnet masks different for each section of the network. So

you'd do it like

subnet 3 192.168.0.0-127 /25
subnet 2 192.168.0.128-159 /27
subnet 1 192.168.0.160-168 /29

now you've addressed all 3 networks and have plenty left

So Classless = VLSM.......?

ncsugrad2002

up2thetime wrote: »

So Classless = VLSM.......?

Exactly

ncsugrad2002

and i just realized a major typo in my example, lol

it's suppose to be a class C subnet..

192.168.10.0 through 192.168.0.255

was suppose to be 192.168.0.x on everything. i messed that up in a few places.. typing too fast i suppose