Subnet Mask & Wildcard Mask Explanation in a Simple Way..!!

 Subnet Mask tells us the number of network bits and the number of host bit present in an IP.

Wildcard mask is used to identify which bits in an IPv4 address to match. In which binary 1 is equal to a match and binary 0 is not a match. 

A Wildcard mask is used in ACL to match the IP address in a better way to permit or deny . and also in some routing protocols, we use wildcard masks to advertise the network such as OSPF etc..!

Wildcard masks use the following rules to match binary 1s and 0s:

• Wildcard mask bit 0: Match the corresponding bit value in the address.

• Wildcard mask bit 1: Ignore the corresponding bit value in the address.

How to calculate the Wildcard mask.??.

Wildcard Mask = 255.255.255.255 - Actual Subnet Mask.

Example-1.

Network=192.168.3.0/24
Subnet Mask=255.255.255.0

Starting value	255.255.255.255
Subtract the subnet mask	–255.255.255. 0
Resulting wildcard mask	0. 0. 0.255

Example 2

Network=192.168.1.0/28
Subnet Mask=255.255.255.240

Starting value	255.255.255.255
Subtract the subnet mask	–255.255.255.240
Resulting wildcard mask	0. 0. 0. 15

Example 3

Network=192.168.1.0/23
Subnet Mask=255.255.254.0

Starting value	255.255.255.255
Subtract the subnet mask	–255.255.254. 0
Resulting wildcard mask	0. 0. 1.255

IPv4 Subnetmask and Wildcardmask Cheetsheet..!

List of wildcard masks

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