前缀长度 /14
/14 的子网掩码是 255.252.0.0
前 14 位是网络位，后 18 位是主机位。
- 子网掩码
- 255.252.0.0
- 二进制
- 11111111.11111100.00000000.00000000
- 通配符掩码
- 0.3.255.255
- 地址总数
- 262,144
- 可用主机数
- 262,142
- 块大小
- 4（第二个八位组）
怎么读这个数
掩码里连续 14 个 1 之后全是 0。写成点分十进制就是 255.252.0.0，第二个八位组是最后一个不满 255 的位置，子网就在这一组里按 4 递增。每个 /14 有 262,144 个地址，去掉网络地址和广播地址，剩 262,142 台主机可用。
通配符掩码 0.3.255.255 是子网掩码按位取反，ACL 和 OSPF 的 network 语句用它：0 表示这一位必须匹配，1 表示不关心。
能切出多少个
- 一个 /8 可以切成 64 个 /14（借 6 位）。
示例：10.0.0.0/8 切成 /14
| # | 网络地址 | 首个可用 | 末个可用 | 广播地址 | 可用主机数 |
|---|---|---|---|---|---|
| 1 | 10.0.0.0/14 | 10.0.0.1 | 10.3.255.254 | 10.3.255.255 | 262,142 |
| 2 | 10.4.0.0/14 | 10.4.0.1 | 10.7.255.254 | 10.7.255.255 | 262,142 |
| 3 | 10.8.0.0/14 | 10.8.0.1 | 10.11.255.254 | 10.11.255.255 | 262,142 |
| 4 | 10.12.0.0/14 | 10.12.0.1 | 10.15.255.254 | 10.15.255.255 | 262,142 |
| 5 | 10.16.0.0/14 | 10.16.0.1 | 10.19.255.254 | 10.19.255.255 | 262,142 |
| 6 | 10.20.0.0/14 | 10.20.0.1 | 10.23.255.254 | 10.23.255.255 | 262,142 |
| 7 | 10.24.0.0/14 | 10.24.0.1 | 10.27.255.254 | 10.27.255.255 | 262,142 |
| 8 | 10.28.0.0/14 | 10.28.0.1 | 10.31.255.254 | 10.31.255.255 | 262,142 |
| 9 | 10.32.0.0/14 | 10.32.0.1 | 10.35.255.254 | 10.35.255.255 | 262,142 |
| 10 | 10.36.0.0/14 | 10.36.0.1 | 10.39.255.254 | 10.39.255.255 | 262,142 |
| 11 | 10.40.0.0/14 | 10.40.0.1 | 10.43.255.254 | 10.43.255.255 | 262,142 |
| 12 | 10.44.0.0/14 | 10.44.0.1 | 10.47.255.254 | 10.47.255.255 | 262,142 |
| 13 | 10.48.0.0/14 | 10.48.0.1 | 10.51.255.254 | 10.51.255.255 | 262,142 |
| 14 | 10.52.0.0/14 | 10.52.0.1 | 10.55.255.254 | 10.55.255.255 | 262,142 |
| 15 | 10.56.0.0/14 | 10.56.0.1 | 10.59.255.254 | 10.59.255.255 | 262,142 |
| 16 | 10.60.0.0/14 | 10.60.0.1 | 10.63.255.254 | 10.63.255.255 | 262,142 |
| 17 | 10.64.0.0/14 | 10.64.0.1 | 10.67.255.254 | 10.67.255.255 | 262,142 |
| 18 | 10.68.0.0/14 | 10.68.0.1 | 10.71.255.254 | 10.71.255.255 | 262,142 |
| 19 | 10.72.0.0/14 | 10.72.0.1 | 10.75.255.254 | 10.75.255.255 | 262,142 |
| 20 | 10.76.0.0/14 | 10.76.0.1 | 10.79.255.254 | 10.79.255.255 | 262,142 |
| 21 | 10.80.0.0/14 | 10.80.0.1 | 10.83.255.254 | 10.83.255.255 | 262,142 |
| 22 | 10.84.0.0/14 | 10.84.0.1 | 10.87.255.254 | 10.87.255.255 | 262,142 |
| 23 | 10.88.0.0/14 | 10.88.0.1 | 10.91.255.254 | 10.91.255.255 | 262,142 |
| 24 | 10.92.0.0/14 | 10.92.0.1 | 10.95.255.254 | 10.95.255.255 | 262,142 |
| 25 | 10.96.0.0/14 | 10.96.0.1 | 10.99.255.254 | 10.99.255.255 | 262,142 |
| 26 | 10.100.0.0/14 | 10.100.0.1 | 10.103.255.254 | 10.103.255.255 | 262,142 |
| 27 | 10.104.0.0/14 | 10.104.0.1 | 10.107.255.254 | 10.107.255.255 | 262,142 |
| 28 | 10.108.0.0/14 | 10.108.0.1 | 10.111.255.254 | 10.111.255.255 | 262,142 |
| 29 | 10.112.0.0/14 | 10.112.0.1 | 10.115.255.254 | 10.115.255.255 | 262,142 |
| 30 | 10.116.0.0/14 | 10.116.0.1 | 10.119.255.254 | 10.119.255.255 | 262,142 |
| 31 | 10.120.0.0/14 | 10.120.0.1 | 10.123.255.254 | 10.123.255.255 | 262,142 |
| 32 | 10.124.0.0/14 | 10.124.0.1 | 10.127.255.254 | 10.127.255.255 | 262,142 |
| 33 | 10.128.0.0/14 | 10.128.0.1 | 10.131.255.254 | 10.131.255.255 | 262,142 |
| 34 | 10.132.0.0/14 | 10.132.0.1 | 10.135.255.254 | 10.135.255.255 | 262,142 |
| 35 | 10.136.0.0/14 | 10.136.0.1 | 10.139.255.254 | 10.139.255.255 | 262,142 |
| 36 | 10.140.0.0/14 | 10.140.0.1 | 10.143.255.254 | 10.143.255.255 | 262,142 |
| 37 | 10.144.0.0/14 | 10.144.0.1 | 10.147.255.254 | 10.147.255.255 | 262,142 |
| 38 | 10.148.0.0/14 | 10.148.0.1 | 10.151.255.254 | 10.151.255.255 | 262,142 |
| 39 | 10.152.0.0/14 | 10.152.0.1 | 10.155.255.254 | 10.155.255.255 | 262,142 |
| 40 | 10.156.0.0/14 | 10.156.0.1 | 10.159.255.254 | 10.159.255.255 | 262,142 |
| 41 | 10.160.0.0/14 | 10.160.0.1 | 10.163.255.254 | 10.163.255.255 | 262,142 |
| 42 | 10.164.0.0/14 | 10.164.0.1 | 10.167.255.254 | 10.167.255.255 | 262,142 |
| 43 | 10.168.0.0/14 | 10.168.0.1 | 10.171.255.254 | 10.171.255.255 | 262,142 |
| 44 | 10.172.0.0/14 | 10.172.0.1 | 10.175.255.254 | 10.175.255.255 | 262,142 |
| 45 | 10.176.0.0/14 | 10.176.0.1 | 10.179.255.254 | 10.179.255.255 | 262,142 |
| 46 | 10.180.0.0/14 | 10.180.0.1 | 10.183.255.254 | 10.183.255.255 | 262,142 |
| 47 | 10.184.0.0/14 | 10.184.0.1 | 10.187.255.254 | 10.187.255.255 | 262,142 |
| 48 | 10.188.0.0/14 | 10.188.0.1 | 10.191.255.254 | 10.191.255.255 | 262,142 |
| 49 | 10.192.0.0/14 | 10.192.0.1 | 10.195.255.254 | 10.195.255.255 | 262,142 |
| 50 | 10.196.0.0/14 | 10.196.0.1 | 10.199.255.254 | 10.199.255.255 | 262,142 |
| 51 | 10.200.0.0/14 | 10.200.0.1 | 10.203.255.254 | 10.203.255.255 | 262,142 |
| 52 | 10.204.0.0/14 | 10.204.0.1 | 10.207.255.254 | 10.207.255.255 | 262,142 |
| 53 | 10.208.0.0/14 | 10.208.0.1 | 10.211.255.254 | 10.211.255.255 | 262,142 |
| 54 | 10.212.0.0/14 | 10.212.0.1 | 10.215.255.254 | 10.215.255.255 | 262,142 |
| 55 | 10.216.0.0/14 | 10.216.0.1 | 10.219.255.254 | 10.219.255.255 | 262,142 |
| 56 | 10.220.0.0/14 | 10.220.0.1 | 10.223.255.254 | 10.223.255.255 | 262,142 |
| 57 | 10.224.0.0/14 | 10.224.0.1 | 10.227.255.254 | 10.227.255.255 | 262,142 |
| 58 | 10.228.0.0/14 | 10.228.0.1 | 10.231.255.254 | 10.231.255.255 | 262,142 |
| 59 | 10.232.0.0/14 | 10.232.0.1 | 10.235.255.254 | 10.235.255.255 | 262,142 |
| 60 | 10.236.0.0/14 | 10.236.0.1 | 10.239.255.254 | 10.239.255.255 | 262,142 |
| 61 | 10.240.0.0/14 | 10.240.0.1 | 10.243.255.254 | 10.243.255.255 | 262,142 |
| 62 | 10.244.0.0/14 | 10.244.0.1 | 10.247.255.254 | 10.247.255.255 | 262,142 |
| 63 | 10.248.0.0/14 | 10.248.0.1 | 10.251.255.254 | 10.251.255.255 | 262,142 |
| 64 | 10.252.0.0/14 | 10.252.0.1 | 10.255.255.254 | 10.255.255.255 | 262,142 |
练一下
给一个地址，前缀都是 /14。先自己算，再展开答案。
第 1 题：10.250.123.166/14 所在的网络、可用范围和广播地址
- 网络地址
10.248.0.0/14- 可用范围
10.248.0.1到10.251.255.254- 广播地址
10.251.255.255- 可用主机
- 262,142
第 2 题：10.117.168.22/14 所在的网络、可用范围和广播地址
- 网络地址
10.116.0.0/14- 可用范围
10.116.0.1到10.119.255.254- 广播地址
10.119.255.255- 可用主机
- 262,142
第 3 题：10.64.150.10/14 所在的网络、可用范围和广播地址
- 网络地址
10.64.0.0/14- 可用范围
10.64.0.1到10.67.255.254- 广播地址
10.67.255.255- 可用主机
- 262,142
第 4 题：10.7.160.96/14 所在的网络、可用范围和广播地址
- 网络地址
10.4.0.0/14- 可用范围
10.4.0.1到10.7.255.254- 广播地址
10.7.255.255- 可用主机
- 262,142
第 5 题：10.238.141.254/14 所在的网络、可用范围和广播地址
- 网络地址
10.236.0.0/14- 可用范围
10.236.0.1到10.239.255.254- 广播地址
10.239.255.255- 可用主机
- 262,142
想多练：按前缀分组的练习题。