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Networking Fundamentals · Foundational

Host Portion

The trailing bits of an IP address that identify a specific interface within a subnet.

Definition

The number of host bits determines subnet size: n host bits give 2^n addresses, of which 2^n minus 2 are usable for hosts in IPv4 because the all-zeros value is the network address and the all-ones value is the broadcast address. Borrowing host bits to create subnets reduces hosts per subnet.

Example

A /26 has 6 host bits, giving 64 addresses and 62 usable hosts.

Exam tip

Host bits all 0 = network ID; all 1 = broadcast; neither can be assigned to a host (except on /31 links).

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