Die Netzmaske, Netzwerkmaske oder Subnetzmaske ist eine Bitmaske, die im Netzwerkprotokoll IPv4 bei der Beschreibung von IP-Netzen angibt, wie viele Bits am Anfang der dargestellten IP-Adresse das Netzpräfix ausmachen.
| / | binary | hex | decimal |
| /1 | 10000000.00000000.00000000.00000000 | 0x80000000 | 128.0.0.0 |
| /2 | 11000000.00000000.00000000.00000000 | 0xc0000000 | 192.0.0.0 |
| /3 | 11100000.00000000.00000000.00000000 | 0xe0000000 | 224.0.0.0 |
| /4 | 11110000.00000000.00000000.00000000 | 0xf0000000 | 240.0.0.0 |
| /5 | 11111000.00000000.00000000.00000000 | 0xf8000000 | 248.0.0.0 |
| /6 | 11111100.00000000.00000000.00000000 | 0xfc000000 | 252.0.0.0 |
| /7 | 11111110.00000000.00000000.00000000 | 0xfe000000 | 254.0.0.0 |
| /8 | 11111111.00000000.00000000.00000000 | 0xff000000 | 255.0.0.0 |
| /9 | 11111111.10000000.00000000.00000000 | 0xff800000 | 255.128.0.0 |
| /10 | 11111111.11000000.00000000.00000000 | 0xffc00000 | 255.192.0.0 |
| /11 | 11111111.11100000.00000000.00000000 | 0xffe00000 | 255.224.0.0 |
| /12 | 11111111.11110000.00000000.00000000 | 0xfff00000 | 255.240.0.0 |
| /13 | 11111111.11111000.00000000.00000000 | 0xfff80000 | 255.248.0.0 |
| /14 | 11111111.11111100.00000000.00000000 | 0xfffc0000 | 255.252.0.0 |
| /15 | 11111111.11111110.00000000.00000000 | 0xfffe0000 | 255.254.0.0 |
| /16 | 11111111.11111111.00000000.00000000 | 0xffff0000 | 255.255.0.0 |
| /17 | 11111111.11111111.10000000.00000000 | 0xffff8000 | 255.255.128.0 |
| /18 | 11111111.11111111.11000000.00000000 | 0xffffc000 | 255.255.192.0 |
| /19 | 11111111.11111111.11100000.00000000 | 0xffffe000 | 255.255.224.0 |
| /20 | 11111111.11111111.11110000.00000000 | 0xfffff000 | 255.255.240.0 |
| /21 | 11111111.11111111.11111000.00000000 | 0xfffff800 | 255.255.248.0 |
| /22 | 11111111.11111111.11111100.00000000 | 0xfffffc00 | 255.255.252.0 |
| /23 | 11111111.11111111.11111110.00000000 | 0xfffffe00 | 255.255.254.0 |
| /24 | 11111111.11111111.11111111.00000000 | 0xffffff00 | 255.255.255.0 |
| /25 | 11111111.11111111.11111111.10000000 | 0xffffff80 | 255.255.255.128 |
| /26 | 11111111.11111111.11111111.11000000 | 0xffffffc0 | 255.255.255.192 |
| /27 | 11111111.11111111.11111111.11100000 | 0xffffffe0 | 255.255.255.224 |
| /28 | 11111111.11111111.11111111.11110000 | 0xfffffff0 | 255.255.255.240 |
| /29 | 11111111.11111111.11111111.11111000 | 0xfffffff8 | 255.255.255.248 |
| /30 | 11111111.11111111.11111111.11111100 | 0xfffffffc | 255.255.255.252 |
| /31 | 11111111.11111111.11111111.11111110 | 0xfffffffe | 255.255.255.254 |
| /32 | 11111111.11111111.11111111.11111111 | 0xffffffff | 255.255.255.255 |