Classless VS Classful understanding?

BeanyBeany Posts: 177Member
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

Comments

  • vishaw1986vishaw1986 Posts: 40Member ■■□□□□□□□□
    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
  • NetworkVeteranNetworkVeteran Posts: 2,338Member
    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.
  • FloOzFloOz Posts: 1,614Member
    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
  • FuturaFutura Posts: 191Member
    '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
  • MickQMickQ Posts: 628Member ■■■■□□□□□□
    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.
  • RouteMyPacketRouteMyPacket Posts: 1,104Member
    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.
    Modularity and Design Simplicity:

    Think of the 2:00 a.m. test—if you were awakened in the
    middle of the night because of a network problem and had to figure out the
    traffic flows in your network while you were half asleep, could you do it?
  • JustFredJustFred Posts: 678Member ■■■□□□□□□□
    I like the RFC's, always a joy to read.
    [h=2]"After a time, you may find that having is not so pleasing a thing, after all, as wanting. It is not logical, but it is often true." Spock[/h]
  • MickQMickQ Posts: 628Member ■■■■□□□□□□
    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.
  • xXErebuSxXErebuS Posts: 230Member
    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.
  • xXErebuSxXErebuS Posts: 230Member
    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.
  • RouteMyPacketRouteMyPacket Posts: 1,104Member
    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!
    Modularity and Design Simplicity:

    Think of the 2:00 a.m. test—if you were awakened in the
    middle of the night because of a network problem and had to figure out the
    traffic flows in your network while you were half asleep, could you do it?
  • FuturaFutura Posts: 191Member
    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.
  • mohamedshajidmohamedshajid Posts: 81Member ■■□□□□□□□□
    Classful address are like this -
    A- 255.0.0.0/8
    B- 255.255.0.0/16
    C- 255.255.255.0/24
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  • MickQMickQ Posts: 628Member ■■■■□□□□□□
    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.
  • fibrefletchfibrefletch Posts: 1Member ■□□□□□□□□□
    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?
  • bharvey92bharvey92 Posts: 419Member
    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 :)
    2018 Goal: CCIE Written [ ]
  • leonlimsgleonlimsg Posts: 10Member ■□□□□□□□□□
    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.
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