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Notable Replies

  1. Hi Rene,

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

    Br
    Zaman

  2. andrew says:

    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 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 10.10.10.248/30, for example, and with a subnet having 50 hosts, you could use 10.10.10.0/26, 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 192.168.0.0/24 and 192.168.1.0/24. These networks have a natural /24 boundary (because they are class C addresses), but I can using CIDR aggregate them via 192.168.0.0/23

  3. Thanks Andrew...,

  4. Here my summary:

    • 255.0.0.0 /8 (8 bits Network, 24 bits Hosts = 2^24 = 256*256*256 = 16.777.216-2)
    • 255.128.0.0 /9 (8+1 = 9 bits Network, 23 bits Hosts = 2^23 = 128*256*256 = 8.388.608-2)
    • 255.192.0.0 /10 (8+2 = 10 bits Network, 22 bits Hosts = 2^22 = 64*256*256 = 2.097.152-2)
    • 255.224.0.0 /11 (8+3 = 11 bits Network, 21 bits Hosts = 2^21 = 32*256*256 = 2.097.152-2)
    • 255.240.0.0 /12 (8+4 = 12 bits Network, 20 bits Hosts = 2^20 = 16*256*256 = 1.048.576-2)
    • 255.248.0.0 /13 (8+5 = 13 bits Network, 19 bits Hosts = 2^19 = 8*256*256 = 524.288-2)
    • 255.252.0.0 /14 (8+6 = 14 bits Network, 18 bits Hosts = 2^18 = 4*256*256 = 262.144-2)
    • 255.254.0.0 /15 (8+7 = 15 bits Network, 17 bits Hosts = 2^17 = 2*256*256 = 131.072-2)
    • 255.255.0.0 /16 (8+8 = 16 bits Network, 16 bits Hosts = 2^16 = 1*256*256 = 65.536-2)
    • 255.255.128.0 /17 (8+8+1 = 17 bits Network, 15 bits Hots = 2^15 = 128*256 = 32768-2)
    • 255.255.192.0 /18 (8+8+2 = 18 bits Network, 14 bits Hots = 2^14 = 64*256 = 16384-2)
    • 255.255.224.0 /19 (8+8+3 = 19 bits Network, 13 bits Hots = 2^13 = 32*256 = 8192-2)
    • 225.225.240.0 /20 (8+8+4 = 20 bits Network, 12 bits Hots = 2^12 = 16*256 = 4096-2)
    • 255.255.248.0 /21 (8+8+5 = 21 bits Network, 11 bits Hots = 2^11 = 8*256 = 2048-2)
    • 255.255.252.0 /22 (8+8+6 = 22 bits Network, 10 bits Hots = 2^10 = 4*256 = 1024-2)
    • 255.255.254.0 /23 (8+8+7 = 23 bits Network, 9 bits Hots = 2^9 = 2*256 = 512-2)
    • 255.255.255.0 /24 (8+8+8 = 24 bits Network , 8 bits Hots = 2^8 = 1*256 = 256-2)
    • 255.255.255.128 /25 (8+8+8+1= 25 bits Network , 7 bits Hots = 2^7 = 128 = 128-2)
    • 255.255.255.192 /26 (8+8+8+2= 26 bits Network , 6 bits Hots = 2^6 = 64 = 64-2)
    • 255.255.255.224 /27 (8+8+8+3= 27 bits Network , 5 bits Hots = 2^5 = 32 = 32-2)
    • 255.255.255.240 /28 (8+8+8+4= 28 bits Network , 4 bits Hots = 2^4 = 16 = 16-2)
    • 255.255.255.248 /29 (8+8+8+5= 29 bits Network , 3 bits Hots = 2^3= 8 = 8-2)
    • 255.255.255.252 /30 (8+8+8+6= 30 bits Network , 2 bits Hots = 2^2= 4 = 4-2)

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