Administrator's Guide

Appendix C. Lists of Reserved Ports, ICMP Types and Codes, and Internet Protocols
The second table shows the IP address interval for each class.
1-set bits Mask IP address class
0 0.0.0.0 0
1 128.0.0.0 1
2 192.0.0.0 2
3 224.0.0.0 3
4 240.0.0.0 4
5 248.0.0.0 5
6 252.0.0.0 6
7 254.0.0.0 7
8 255.0.0.0 0
9 255.128.0.0 1
10 255.192.0.0 2
11 255.224.0.0 3
12 255.240.0.0 4
13 255.248.0.0 5
14 255.252.0.0 6
15 255.254.0.0 7
16 255.255.0.0 0
17 255.255.128.0 1
18 255.255.192.0 2
19 255.255.224.0 3
20 255.255.240.0 4
21 255.255.248.0 5
22 255.255.252.0 6
23 255.255.254.0 7
24 255.255.255.0 0
25 255.255.255.128 1
26 255.255.255.192 2
27 255.255.255.224 3
28 255.255.255.240 4
29 255.255.255.248 5
30 255.255.255.252 6
31 255.255.255.254 7
32 255.255.255.255 8
Example: We want to split the network 130.234.250.0/25 (i.e., 130.234.250.0-
130.234.250.127) into four subnets. The netmask for each subnet will be 27
bits, which means 255.255.255.224. This netmask is in IP class 3. The second
table gives us the following available intervals: 0-31, 32-63, 64-95, and 96-127
(then we are out of IP addresses). One of the subnets will be 130.234.250.64/27
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