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Forum Replies

  1. James,
    Only the first four bits (3 really, since E class isn't used) in the first octet determine class (as shown in the table below). You are correct in your example about

    Keep in mind, however, that "class" doesn't really mean anything anymore. This is an outdated term that nobody really uses now. Even Cisco has stopped bothering to test on it!

    Binary (first 4 bits) Class
    0000                   A
    1000                   B
    1100                   C
    1110                   D
    1111                   E
  2. Hi Rene,

    What do you mean by CIDR & VLSM ? The both are same or what is the difference between them.


  3. andrew says:

    These can be easily confused--in fact I had to review them myself to make sure I am giving you accurate information.

    VLSM is aptly named, because it means using a subnet mask of variable lengths throughout your organization with the same network block. For example, suppose your ISP has given you as an IP range. Without VLSM, you would have to pick a certain subnet mask, say, (/28) and stick with that. So if you wanted to use this block throughout your company, you would always have to use /28. This becomes wasteful in the case where you have a subnet with just two hosts, or it becomes inadequate where you have a subnet with 50 hosts. With VSLM, you have the freedom to change your subnet mask as needed, so in the case of a subnet with two hosts, you could use, for example, and with a subnet having 50 hosts, you could use, for example.

    CIDR is basically "supernetting." This is where you can aggregate networks together into larger networks beyond their natural network boundary. For example, suppose I have and These networks have a natural /24 boundary (because they are class C addresses), but I can using CIDR aggregate them via

  4. Thanks Andrew...,

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