| Ingate Firewall 4.2: User Manual | ||
|---|---|---|
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This is a list of the IP addresses available for different netmasks. The first column shows the number of bits used for the net address, i. e., is set to 1 in the netmask. The second column maps the number of bits to a netmask on the usual octet-dot format. The third column shows the address class for this netmask.
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 (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 | |
| 7 | 0-1 | 2-3 | 4-5 | 6-7 | 8-9 | 10-11 | ... | 254-255 |
| 8 | 0 | 1 | 2 | 3 | 4 | 5 | ... | 255 |
You could have a large network, for example 130.234.128.0/18, which is interpreted from the tables as all IP addresses from 130.234.128.0 to 130.234.191.255, inclusive (18 is in class no. 2, giving an IP interval of 128-191). N.B.: The netmask only reaches the third byte, which means that all IP addresses in byte 4 are available.
The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private internets (see also RFC 1918):
10.0.0.0 - 10.255.255.255 (10/8)
172.16.0.0 - 172.31.255.255 (172.16/12)
192.168.0.0 - 192.168.255.255 (192.168/16)