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    Network CIDR Notation

    13 agosto 2020

    [et_pb_section fb_built=”1″ _builder_version=”4.4.6″ custom_margin=”||0px|||”][et_pb_row _builder_version=”4.4.6″][et_pb_column type=”4_4″ _builder_version=”4.4.6″][et_pb_text _builder_version=”4.4.6″ hover_enabled=”0″] Many firewalls and network devices use CIDR (Classless Inter-Domain Routing) notation rather than the common subnet mask 255.x.x.x when configuring addresses and networks. Refer to the CIDR Subnet Table to find the CIDR equivalent of a decimal subnet mask. [/et_pb_text][/et_pb_column][/et_pb_row][et_pb_row _builder_version=”4.4.6″][et_pb_column type=”4_4″ _builder_version=”4.4.6″][et_pb_text _builder_version=”4.4.6″ hover_enabled=”0″]

    CIDR Subnet Table

    Subnet Mask CIDR Prefix Total IP Addresses Usable IP Addresses Number of /24 networks

    255.255.255.255 /32 1 1 1/256th

    255.255.255.254 /31 2 2* 1/128th

    255.255.255.252 /30 4 2 1/64th

    255.255.255.248 /29 8 6 1/32nd

    255.255.255.240 /28 16 14 1/16th

    255.255.255.224 /27 32 30 1/8th

    255.255.255.192 /26 64 62 1/4th

    255.255.255.128 /25 128 126 1 half

    255.255.255.0 /24 256 254 1

    255.255.254.0 /23 512 510 2

    255.255.252.0 /22 1024 1022 4

    255.255.248.0 /21 2048 2046 8

    255.255.240.0 /20 4096 4094 16

    255.255.224.0 /19 8192 8190 32

    255.255.192.0 /18 16,384 16,382 64

    255.255.128.0 /17 32,768 32,766 128

    255.255.0.0 /16 65,536 65,534 256

    255.254.0.0 /15 131,072 131,070 512

    255.252.0.0 /14 262,144 262,142 1024

    255.248.0.0 /13 524,288 524,286 2048

    255.240.0.0 /12 1,048,576 1,048,574 4096

    255.224.0 0 /11 2,097,152 2,097,150 8192

    255.192.0.0 /10 4,194,304 4,194,302 16,384

    255.128.0.0 /9 8,388,608 8,388,606 32,768

    255.0.0.0 /8 16,777,216 16,777,214 65,536

    254.0.0.0 /7 33,554,432 33,554,430 131,072

    252.0.0.0 /6 67,108,864 67,108,862 262,144

    248.0.0.0 /5 134,217,728 134,217,726 1,048,576

    240.0.0.0 /4 268,435,456 268,435,454 2,097,152

    224.0.0.0 /3 536,870,912 536,870,910 4,194,304

    192.0.0.0 /2 1,073,741,824 1,073,741,822 8,388,608

    128.0.0.0 /1 2,147,483,648 2,147,483,646 16,777,216

    0.0.0.0 /0 4,294,967,296 4,294,967,294 33,554,432

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    Where do CIDR numbers come from? The CIDR number comes from the number of ones in the subnet mask when converted to binary. The common subnet mask 255.255.255.0 is 11111111.11111111.11111111.00000000 in binary. This adds up to 24 ones, or /24 (pronounced ‘slash twenty four’). A subnet mask of 255.255.255.192 is 11111111.11111111.11111111.11000000 in binary, or 26 ones, hence /26.

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