Classless VS Classful understanding?

Morning,

Sometimes I come across a topic that I can't get my head around, this is one of them.

Understand some of the routing protocol concepts but i need some help on the above.

In basic terms plz, can someone explain classless and Classful to me with examples? Differences etc

Don't want to move on until I understand this completely, ta

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Comments

vishaw1986

Very basis example :

Suppose you have 254 users in your network and you want a subnet for them
i.e 192.168.1.0/24 ---- its classfull

Time being your requirement get changed you want partition in your network for some reason in 100 , 50 , 50
if you use classfull then
192.168.1.0/24 for 100
192.168.2.0/26 for 50
and so on ....

Now let come to classless

Only one subnet required
192.168.1.0/25 ---for 100
192.168.1.128/26 ---for 50
192.168.1.192/26 -- for 50

It means we save two subnet with the help fof classless ......
Moreover in classfull we don't have the subnet information in the update and in classless we have the same .

Hope this help you

Ivanjam

http://www.techexams.net/forums/ccna-ccent/61220-classful-vs-classless.html

http://www.techexams.net/forums/ccna-ccent/46974-classless-vs-classful-regards-rip.html

http://www.techexams.net/forums/ccna-ccent/42661-subnetting-exam-questions-classful-vs-cidr.html

http://www.techexams.net/forums/ccna-ccent/4894-classful-vs-classless-routing-protocol.html

NetworkVeteran

Beany wrote: »

In basic terms plz, can someone explain classless and Classful to me with examples? Differences etc. Don't want to move on until I understand this completely, ta

If you want to understand this completely, you might begin with RFC 790 & 791 (classful addressing), RFC 940 & 1219 (subnetting), RFC 1518 & 1878 (VLSM & CIDR), RFC 1918 (private addressing) plus the links that Ivan posted above. Enjoy.

If you're having trouble understanding the limited amount of these topics covered by the ICND1/ICND2, you might begin by explaining your understanding of these concepts, and where precisely you are confused so that we can better help you.

FloOz

Classless address abide to the rules of using Class A subnet masks with Class A addresses. For example:
Class A - 10.0.0.0/8 (255..0.0.0)
Class B - 172.123.0.0/12 (255.255.0.0)
Class C - 192.168.123.0/24 (255.255.255.0)

Classful Ranges (Rememeber your looking at the first octet)
Class A - 1-126
Class B - 128-191
Class C - 192-223

So all Class A address will have a 255.0.0.0 mask; Class B will have 255.255.0.0 mask; Class C will have 255.255.255.0

As for Classless addressing they do not follow the above rules. For example

10.0.0.0.0/20
172.123.0.0/30
192.168.123.0/15

Hope this helps you out

Futura

'Less is more' that's the way i remember it!

If you are advertising a Classfull its 192.168.x.x or 172.16.x.x etc.

If its classless then you could advertise a 192.168.32.0 and a 192.168.64.0 etc,etc, more subnets

MickQ

Classful: class-full. It's the full IP address class range. E.g. wanting to advertise 10.0.1.0 /24 would end up being the full 10.0.0.0 /8.

Classless: class...less a bit

Sends that little bit of the class range that you specify; it's less than full. E.g. you want to advertise 10.0.1.0 /24, it ends up being... 10.0.1.0 /24.

RouteMyPacket

I'm coming into certifications with experience and I for one have only used CIDR, it sucks to see classful questions on the exams.

Am I the only one that see's that as a waste of time? When I was in school of course we learned about classful so I understand it no problem but its a thing of the past.

JustFred

I like the RFC's, always a joy to read.

MickQ

Yes, they are mainly a thing of the past, but the best way to understand the current state of things is by learning from the past. Besides, you never know when something "legacy" will rear its ugly head.

xXErebuS

Futura wrote: »

'Less is more' that's the way i remember it!

If you are advertising a Classfull its 192.168.x.x or 172.16.x.x etc.

If its classless then you could advertise a 192.168.32.0 and a 192.168.64.0 etc,etc, more subnets

192.168.32.0/24 and 192.168.64.0/24 both qualify as classful.

xXErebuS

RouteMyPacket wrote: »

I'm coming into certifications with experience and I for one have only used CIDR, it sucks to see classful questions on the exams.

Am I the only one that see's that as a waste of time? When I was in school of course we learned about classful so I understand it no problem but its a thing of the past.

Its not a waste of time when you forget the no auto summary command and wonder why you are having issues with your 10.10.10.0/24 and 10.88.0.0/16 routes.

RouteMyPacket

This is a tough one, it's completely useless because well, it's a thing of the past and yet as mentioned above, having known it from the past doesn't hurt. I just hate the fact that when I study for a test and have to sit an exam I am restudying and answering those types of questions. Ugh!

Futura

xXErebuS wrote: »

192.168.32.0/24 and 192.168.64.0/24 both qualify as classful.

sorry, Shoud have been more specific, the reason I put 32 and 64 is because I thought you would have sussed the mask of 255.255.224.0 would be used to make it classless.

I do this everyday for my work and sometimes presume people know what I mean.

mohamedshajid

Classful address are like this -
A- 255.0.0.0/8
B- 255.255.0.0/16
C- 255.255.255.0/24

MickQ

mohamedshajid wrote: »

Classful address are like this -
A- 255.0.0.0/8
B- 255.255.0.0/16
C- 255.255.255.0/24

No, they're the classful subnets. They apply to the IP class addresses as you noted by A/B/C.

The addresses for private (RFC 1918 ) addresses are:
A. 10.0.0.0 /8
B. 172.16.0.0 /16 ....... up to 172.32.0.0 /16
C. 192.168.0.0 /24 ...... up to 192.168.255.0 /24

Where A,B,C are the IP class address range type.

fibrefletch

Hi

I have seen the terms 'classless' and 'classful' sub-netting and also 'fixed' sub-netting and I imagine this as the following. (assumes a familiarity with VLSM and CIDR)

VLSM is ‘classful’ sub-netting in that it does not break the IPv4 address class rules and intrude on the network bits (class A, B or C), but of course it can borrow host bits to extend the mask, and so make it a 'variable' mask.

Fixed sub-netting is a variation on the above but means that all subnets created in the network are the same size and not variable, with the same number of hosts, using the same length of mask (wasteful for a WAN link!) Note, this is still 'classful' sub-netting also

Now CIDR (based on VLSM) is ‘classless’ sub-netting because you break the ‘normal’ network boundary rule and intrude on what are normally network bits, so you might see an address mask such as 193.1.96.0 /20

Can I get some expert agreement here?

bharvey92

Hi Beany

Classful routing protocols do not send there subnet masks which means they cannot support VLSM (eg: RIP, IGRP)
Classless send subnet masks which means they support VLSM (OSPF, EIGRP)

Hope this helps

leonlimsg

Classful routing can affect discontiguous network.

Let's say we have the following set up and configuration:

RouterA s0/0 - s0/0 RouterX s0/1 - s0/1RouterB

- all routers are using RIP routing
- RouterA has a LAN network of 172.16.1.0/24
- RouterB has a LAN network of 172.16.3.0/24

Since all routers are using RIP and RIP does not support classless routing, RouterA and RouterB will send routing updates in CLASSFUL format. Instead of sending 172.16.1.0/24, it will send 172.16.0.0/16 to RouterX.

Sp RouterA send 172.16.0.0/16 and RouterB also send 172.16.0.0/16 to RouterX.

RouterX is confused because there are two outgoing interfaces to 172.16.0.0! Let's say a data to 172.16.0.0 has to pass through RouterX, RouterX will have a big problem because it cannot identify the correct interface to send out.