A value used to divide an IP address into a network portion and a host portion.
A bitmask that marks how much of an IP address is the network portion versus the host portion. 255.255.255.0, for example, means the first 24 bits are the network portion -- the same information as CIDR notation's /24. It's used to determine whether two hosts are on the same segment; a misconfigured mask can prevent hosts that should be able to communicate from doing so.
© 2026 ITBGM