Subnet mask and wildcard mask are two important components to identify different networks in computer networking, and must be configured correctly to transfer data to intended nodes of the network. We assign the subnet mask will configuring the IP address on the device, but we do not explicitly configure a wildcard mask to any device. Both are 32 bits long masks and prove helpful by giving information about the different parts of an IP address. But they are different from each other in every sense, in their concept, in their format, and their usage.
A subdivided network (subnet) is implemented to avoid wastage of IP addresses over a network. Its main use is to identify the network and hosts. IP addresses on the same subnet are not separated by a router, whereas, IP addresses on different subnets must be separated by one router. One major point to keep in mind for the subnet mask is that the 1’s and 0’s must be contagious. For example, the subnet mask for a classful Class A IP address is 255.0.0.0, which can also be written as 11111111.00000000.00000000.00000000 in the binary form, and also as /8 in the prefix form. In this subnet mask, the 1’s identify the network part of the address and the 0’s identify the host part. As long as the number in the first octet, or say, the number corresponding the 1’s, matches, the IP addresses are considered to be on the same network. For subnet mask 255.255.255.255, all the bits of an IP address must match, and for subnet mask 0.0.0.0, none of the bits should match.
A wildcard mask is generally said to be an inverted subnet mask. Its main use is to let the IOS know whether to compare the corresponding P address bits or to ignore them. To calculate a wildcard mask, just subtract the number in every octet from 255. For example, for a subnet mask 255.0.0.0, the corresponding wildcard mask would be 0.0.0.255, which can also be written as 00000000.00000000.00000000.11111111 in the binary form. A wildcard mask cares about the number corresponding to the 0’s and does not care about the number corresponding to 1’s. In this, to implement a given command, the IP address part corresponding to 0’s must match. Moreover, the 1’s and 0’s should not necessarily be contagious in a wildcard mask. For instance, 0.3.0.15 (00000000.00000011.00000000.00001111) is a valid wildcard mask but there is no corresponding subnet mask for this. A wildcard mask generally specifies a range of IP addresses. For wildcard mask 0.0.0.0, the entire IP address must be compared, and for wildcard mask 255.255.255.255, no bits of the IP address be compared. Wildcard mask has found a special functionality in the access control lists (ACLs) and routing protocols like OSPF, EIGRP, and BGP.
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