- Net & Subnet Masks
- Used to determine which bits of an IP Address are network bits and which are host bits
Wildcard Masks
An alternative way of depicting a subnet mask. Basically an ‘inverted’ subnet mask i.e. all 1s in the subnet mask are 0s in the wildcard mask and vice-versa.
Wildcard masks are used to make comparisons between two IP addresses. Commonly, they are used by Dynamic Routing protocols, for instance EIGRP and OSPF, to indicate which IP addresses should be dynamically routed, among other purposes.
Wildcard masks use a matching rule:
- ‘0’ in the mask means the two corresponding bits in the compared addresses must match
- ’1’ in the mask means it doesn’t matter if the corresponding bits match or not (they are wildcards)
Ex.1:
(Subnet Mask) 11111111.11111111.11111111.00000000=255.255.255.0(Wildcard Mask) 00000000.00000000.00000000.11111111=0.0.0.255=/24
Ex.2:
(Subnet Mask) 11111111.11111100.00000000.00000000=255.252.0.0(Wildcard Mask) 00000000.00000011.11111111.11111111=0.3.255.255=/14
Ex.3:
(Subnet Mask) 11111111.11111111.11100000.00000000=255.252.224.0(Wildcard Mask) 00000000.00000000.00011111.11111111=0.0.31.255=/19
| Slash | Netmask | Wildcard mask |
|---|---|---|
| /32 | 255.255.255.255 | 0.0.0.0 |
| /31 | 255.255.255.254 | 0.0.0.1 |
| /30 | 255.255.255.252 | 0.0.0.3 |
| /29 | 255.255.255.248 | 0.0.0.7 |
| /28 | 255.255.255.240 | 0.0.0.15 |
| /27 | 255.255.255.224 | 0.0.0.31 |
| /26 | 255.255.255.192 | 0.0.0.63 |
| /25 | 255.255.255.128 | 0.0.0.127 |
| /24 | 255.255.255.0 | 0.0.0.255 |
| /23 | 255.255.254.0 | 0.0.1.255 |
| /22 | 255.255.252.0 | 0.0.3.255 |
| /21 | 255.255.248.0 | 0.0.7.255 |
| /20 | 255.255.240.0 | 0.0.15.255 |
| /19 | 255.255.224.0 | 0.0.31.255 |
| /18 | 255.255.192.0 | 0.0.63.255 |
| /17 | 255.255.128.0 | 0.0.127.255 |
| /16 | 255.255.0.0 | 0.0.255.255 |
| /15 | 255.254.0.0 | 0.1.255.255 |
| /14 | 255.252.0.0 | 0.3.255.255 |
| /13 | 255.248.0.0 | 0.7.255.255 |
| /12 | 255.240.0.0 | 0.15.255.255 |
| /11 | 255.224.0.0 | 0.31.255.255 |
| /10 | 255.192.0.0 | 0.63.255.255 |
| /9 | 255.128.0.0 | 0.127.255.255 |
| /8 | 255.0.0.0 | 0.255.255.255 |
| /7 | 254.0.0.0 | 1.255.255.255 |
| /6 | 252.0.0.0 | 3.255.255.255 |
| /5 | 248.0.0.0 | 7.255.255.255 |
| /4 | 240.0.0.0 | 15.255.255.255 |
| /3 | 224.0.0.0 | 31.255.255.255 |
| /2 | 192.0.0.0 | 63.255.255.255 |
| /1 | 128.0.0.0 | 127.255.255.255 |
| /0 | 0.0.0.0 | 255.255.255.255 |