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Forum Replies

  1. Rene,

    Hello, the command “ip classless” is something I have always seen on Cisco routers but never understood what it does. Can you explain this command?

    Thanks,

    Chris

  2. 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 171.15.85.0/24.

    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 This is an outdated term that nobody really uses now.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
    

  3. Zaman,
    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 10.10.10.0/24 as an IP range. Without VLSM, you would have to pick a certain subnet mask, say, 255.255.255.240 (/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

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