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Glossary

stub area

An OSPF area carrying a default route, intra-area routes, and

interarea routes, but no external routes. Configuration of virtual links
cannot be achieved across a stub area, and stub areas are not allowed to con-
tain an ASBR. See also: non-stub area, ASBR, and OSPF.

stub network

A network having only one connection to a router.

STUN

Serial Tunnel: A technology used to connect an HDLC link to an

SDLC link over a serial link.

subarea

A portion of an SNA network made up of a subarea node and its

attached links and peripheral nodes.

subarea node

An SNA communications host or controller that handles

entire network addresses.

subchannel

A frequency-based subdivision that creates a separate broad-

band communications channel.

subinterface

One of many virtual interfaces available on a single physical

interface.

subnet

See: subnetwork.

subnet address

The portion of an IP address that is specifically identified

by the subnet mask as the subnetwork. See also: IP address, subnetwork, and
subnet mask.

subnet mask

Also simply known as mask, a 32-bit address mask used in

IP to identify the bits of an IP address that are used for the subnet address.
Using a mask, the router does not need to examine all 32 bits, only those
selected by the mask. See also: address mask and IP address.

subnetting

Used in IP networks to break up larger networks into smaller

subnetworks.

subnetwork

1) Any network that is part of a larger IP network and is iden-

tified by a subnet address. A network administrator segments a network into
subnetworks in order to provide a hierarchical, multilevel routing structure,
and at the same time protect the subnetwork from the addressing complexity
of networks that are attached. Also known as a subnet. See also: IP address,
subnet mask, and subnet address. 2) In OSI networks, the term specifically

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