10進数、２進数,16進数の各々の関係とサブネットマスクの早見表

10進数、2進数、16進数の各々の関係と、サブネットマスクの早見表です。

IPアドレスの概念も2進数（ビット）で考えられるようになると理解がぐっと進みます。

## 【早見表1】 10進数の0〜127までとサブネットマスク対応表

| 10進 | 2進 | 16進 | 第3オクテット | 割り当てIP | 第4オクテット | 割り当てIP |
| —: | :— | :— | :— | —: | :— | —: |
| 0 | 00000000 | 00 | /16 | 65536 | /24 | 128 |
| 1 | 00000001 | 01 | | | /25 | |
| 2 | 00000010 | 02 | | | | |
| 3 | 00000011 | 03 | | | | |
| 4 | 00000100 | 04 | | | | |
| 5 | 00000101 | 05 | | | | |
| 6 | 00000110 | 06 | | | | |
| 7 | 00000111 | 07 | | | | |
| 8 | 00001000 | 08 | | | | |
| 9 | 00001001 | 09 | | | | |
| 10 | 00001010 | 0A | | | | |
| 11 | 00001011 | 0B | | | | |
| 12 | 00001100 | 0C | | | | |
| 13 | 00001101 | 0D | | | | |
| 14 | 00001110 | 0E | | | | |
| 15 | 00001111 | 0F | | | | |
| 16 | 00010000 | 10 | | | | |
| 17 | 00010001 | 11 | | | | |
| 18 | 00010010 | 12 | | | | |
| 19 | 00010011 | 13 | | | | |
| 20 | 00010100 | 14 | | | | |
| 21 | 00010101 | 15 | | | | |
| 22 | 00010110 | 16 | | | | |
| 23 | 00010111 | 17 | | | | |
| 24 | 00011000 | 18 | | | | |
| 25 | 00011001 | 19 | | | | |
| 26 | 00011010 | 1A | | | | |
| 27 | 00011011 | 1B | | | | |
| 28 | 00011100 | 1C | | | | |
| 29 | 00011101 | 1D | | | | |
| 30 | 00011110 | 1E | | | | |
| 31 | 00011111 | 1F | | | | |
| 32 | 00100000 | 20 | | | | |
| 33 | 00100001 | 21 | | | | |
| 34 | 00100010 | 22 | | | | |
| 35 | 00100011 | 23 | | | | |
| 36 | 00100100 | 24 | | | | |
| 37 | 00100101 | 25 | | | | |
| 38 | 00100110 | 26 | | | | |
| 39 | 00100111 | 27 | | | | |
| 40 | 00101000 | 28 | | | | |
| 41 | 00101001 | 29 | | | | |
| 42 | 00101010 | 2A | | | | |
| 43 | 00101011 | 2B | | | | |
| 44 | 00101100 | 2C | | | | |
| 45 | 00101101 | 2D | | | | |
| 46 | 00101110 | 2E | | | | |
| 47 | 00101111 | 2F | | | | |
| 48 | 00110000 | 30 | | | | |
| 49 | 00110001 | 31 | | | | |
| 50 | 00110010 | 32 | | | | |
| 51 | 00110011 | 33 | | | | |
| 52 | 00110100 | 34 | | | | |
| 53 | 00110101 | 35 | | | | |
| 54 | 00110110 | 36 | | | | |
| 55 | 00110111 | 37 | | | | |
| 56 | 00111000 | 38 | | | | |
| 57 | 00111001 | 39 | | | | |
| 58 | 00111010 | 3A | | | | |
| 59 | 00111011 | 3B | | | | |
| 60 | 00111100 | 3C | | | | |
| 61 | 00111101 | 3D | | | | |
| 62 | 00111110 | 3E | | | | |
| 63 | 00111111 | 3F | | | | |
| 64 | 01000000 | 40 | | | | |
| 65 | 01000001 | 41 | | | | |
| 66 | 01000010 | 42 | | | | |
| 67 | 01000011 | 43 | | | | |
| 68 | 01000100 | 44 | | | | |
| 69 | 01000101 | 45 | | | | |
| 70 | 01000110 | 46 | | | | |
| 71 | 01000111 | 47 | | | | |
| 72 | 01001000 | 48 | | | | |
| 73 | 01001001 | 49 | | | | |
| 74 | 01001010 | 4A | | | | |
| 75 | 01001011 | 4B | | | | |
| 76 | 01001100 | 4C | | | | |
| 77 | 01001101 | 4D | | | | |
| 78 | 01001110 | 4E | | | | |
| 79 | 01001111 | 4F | | | | |
| 80 | 01010000 | 50 | | | | |
| 81 | 01010001 | 51 | | | | |
| 82 | 01010010 | 52 | | | | |
| 83 | 01010011 | 53 | | | | |
| 84 | 01010100 | 54 | | | | |
| 85 | 01010101 | 55 | | | | |
| 86 | 01010110 | 56 | | | | |
| 87 | 01010111 | 57 | | | | |
| 88 | 01011000 | 58 | | | | |
| 89 | 01011001 | 59 | | | | |
| 90 | 01011010 | 5A | | | | |
| 91 | 01011011 | 5B | | | | |
| 92 | 01011100 | 5C | | | | |
| 93 | 01011101 | 5D | | | | |
| 94 | 01011110 | 5E | | | | |
| 95 | 01011111 | 5F | | | | |
| 96 | 01100000 | 60 | | | | |
| 97 | 01100001 | 61 | | | | |
| 98 | 01100010 | 62 | | | | |
| 99 | 01100011 | 63 | | | | |
| 100 | 01100100 | 64 | | | | |
| 101 | 01100101 | 65 | | | | |
| 102 | 01100110 | 66 | | | | |
| 103 | 01100111 | 67 | | | | |
| 104 | 01101000 | 68 | | | | |
| 105 | 01101001 | 69 | | | | |
| 106 | 01101010 | 6A | | | | |
| 107 | 01101011 | 6B | | | | |
| 108 | 01101100 | 6C | | | | |
| 109 | 01101101 | 6D | | | | |
| 110 | 01101110 | 6E | | | | |
| 111 | 01101111 | 6F | | | | |
| 112 | 01110000 | 70 | | | | |
| 113 | 01110001 | 71 | | | | |
| 114 | 01110010 | 72 | | | | |
| 115 | 01110011 | 73 | | | | |
| 116 | 01110100 | 74 | | | | |
| 117 | 01110101 | 75 | | | | |
| 118 | 01110110 | 76 | | | | |
| 119 | 01110111 | 77 | | | | |
| 120 | 01111000 | 78 | | | | |
| 121 | 01111001 | 79 | | | | |
| 122 | 01111010 | 7A | | | | |
| 123 | 01111011 | 7B | | | | |
| 124 | 01111100 | 7C | | | | |
| 125 | 01111101 | 7D | | | | |
| 126 | 01111110 | 7E | | | | |
| 127 | 01111111 | 7F | | | | |

## 【早見表2】 サブネットマスクを基準に抽出したもの

| 10進 | 2進 | 16進 | 第3オクテット | 割り当てIP | 第4オクテット | 割り当てIP |
| —: | :— | :— | :— | —: | :— | —: |
| 0 | 00000000 | 00 | ○ /16 | 65536 | /24 | 128 |
| 128 | 10000000 | 80 | ○ /17 | 32768 | /25 | 64 |
| 192 | 11000000 | C0 | ○ /18 | 16384 | /26 | 32 |
| 224 | 11100000 | E0 | ○ /19 | 8192 | /27 | 16 |
| 240 | 11110000 | F0 | ○ /20 | 4096 | /28 | 8 |
| 248 | 11111000 | F8 | ○ /21 | 2048 | /29 | 4 |
| 252 | 11111100 | FC | ○ /22 | 1024 | /30 | 2 |
| 254 | 11111110 | FE | ○ /23 | 512 | /31 | 1 |
| 255 | 11111111 | FF | ○ /24 | 256 | /32 | 0 |