Netmask
A netmask is a bit mask that distinguishes the network portion of an IP address from its host portion.
Acing the CCNA Exam: Volume 1 Fundamentals and Protocols
A netmask is a 32-bit value paired with an IPv4 address to identify which address bits belong to the network portion and which belong to the host portion.
- How it is used
- Defines IPv4 network and host boundaries and supplies the dotted-decimal form required for Cisco IOS configuration.
- How deep it goes
- Explains bit positions, dotted-decimal conversion, subnet calculations, and interface configuration, while deferring broader subnet design details.
- Examples
- Uses /24 router interfaces, a /16 bit diagram, a /28 network-address exercise, and /26 subnet attributes.
- What you can do after
- Apply it via Cisco IOS commands, convert prefix lengths, identify network boundaries, and solve subnet-address and usable-range questions.
Read how Acing the CCNA Exam: Volume 1 Fundamentals and Protocols explains netmask →
Acing the CCNA Exam: Volume 2 Advanced Networking and Security
A netmask is a bit mask that separates the network portion of an IP address from its host portion.
- How it is used
- Determines whether hosts treat destinations as local-LAN addresses or send them through the default gateway.
- How deep it goes
- Defines the netmask and interprets dotted-decimal, hexadecimal, and prefix-length forms, without deriving bitwise operations.
- Examples
- Uses macOS and Linux `ifconfig`, `ip addr`, and routing output to show 255.255.255.0, 0xffffff00, and /24.
- What you can do after
- Evaluate/understand host and routing output by identifying the netmask and its associated local LAN.
Read how Acing the CCNA Exam: Volume 2 Advanced Networking and Security explains netmask →
Related concepts
- classless inter-domain routingused by · Classless Inter-Domain Routing is an IP addressing and routing scheme that represents networks and address ranges with a network prefix and prefix length.
- prefix lengthequivalent to · A prefix length is the number of leading bits in an IP address that define its network portion, conventionally expressed in slash notation.
- wildcard maskcontrasts with · A wildcard mask is a 32-bit bit mask in which zero bits require corresponding address bits to match and one bits ignore them during address matching.
- network portionmeasures · The network portion is the part of an IP address, determined by its prefix or subnet mask, that identifies the network or subnet containing the addressed host.
- IP addressconfigures · An IP address is a numerical address used by the Internet Protocol to identify a network interface and support packet delivery across networks.
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