Subnet masks

We've just covered the various classes of IPv4 address spaces, but there are times when using those classes of address space might not be appropriate. The fact of the matter is that Class A, B, and C are classful address spaces if we use the default subnet mask for those classes of IPs. For instance, a Class A uses a subnet mask of 255.0.0.0. But wait, what is a subnet mask? To begin with, a subnet mask identifies the network portion and the host portion of a given IP address. This includes both IPv4 and IPv6. A subnet mask enables us to easily find out the network address for a given IP address. A subnet mask is often written in dotted decimal format. However, it is possible to represent a subnet mask in a slash notation; namely, ...

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