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Appendix C. Lists of Reserved Ports, ICMP Types and Codes, and Internet Protocols
1-set bits Mask IP address class
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 (130.234.250.64-130.234.250.95).
Class IP
intervals
0 0-255
1 0-127 128-255
2 0-63 64-127 128-191 192-255
3 0-31 32-63 64-95 96-127 128-159 160-191 192-223 224-255
4 0-15 16-31 32-47 48-63 64-79 80-95 96-111 112-127
128-143 144-159 160-175 176-191 192-207 208-223 224-239 240-255
5 0-7 8-15 16-23 24-31 32-39 40-47 48-55 56-63
64-71 72-79 80-87 88-95 96-103 104-111 112-119 120-127
128-135 136-143 144-151 152-159 160-167 168-175 176-183 184-191
192-199 200-207 208-215 216-223 224-231 232-239 240-247 248-255
6 0-3 4-7 8-11 12-15 16-19 20-23 24-27 28-31
32-35 36-39 40-43 44-47 48-51 52-55 56-59 60-63
64-67 68-71 72-75 76-79 80-83 84-87 88-91 92-95
96-99 100-103 104-107 108-111 112-115 116-119 120-123 124-127
128-131 132-135 136-139 140-143 144-147 148-151 152-155 156-159
160-163 164-167 168-171 172-175 176-179 180-183 184-187 188-191
192-195 196-199 200-203 204-207 208-211 212-215 216-219 220-223
224-227 228-231 232-235 236-239 240-243 244-247 248-251 252-255
138