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Glossary

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Spanning Tree Protocol (STP)

The bridge protocol (IEEE 802.1D) that

enables a learning bridge to dynamically avoid loops in the network
topology by creating a spanning tree using the spanning-tree algorithm.
Spanning-tree frames called Bridge Protocol Data Units (BPDUs) are sent
and received by all switches in the network at regular intervals. The switches
participating in the spanning tree don't forward the frames; instead, they're
processed to determine the spanning-tree topology itself. Cisco Catalyst
series switches use STP 802.1D to perform this function. See also: BPDU,
learning bridge, MAC address, spanning tree, and spanning-tree algorithm.

SPF

Shortest Path First algorithm: A routing algorithm used to decide on

the shortest-path spanning tree. Sometimes called Dijkstra's algorithm and
frequently used in link-state routing algorithms. See also: link-state routing
algorithm.

SPID

Service Profile Identifier: A number assigned by service providers or

local telephone companies and assigned by administrators to a BRI port.
SPIDs are used to determine subscription services of a device connected via
ISDN. ISDN devices use SPID when accessing the telephone company switch
that initializes the link to a service provider.

split horizon

Useful for preventing routing loops, a type of distance-vector

routing rule where information about routes is prevented from leaving the
router interface through which that information was received.

spoofing

1) In dial-on-demand routing (DDR), where a circuit-switched

link is taken down to save toll charges when there is no traffic to be sent,
spoofing is a scheme used by routers that causes a host to treat an interface
as if it were functioning and supporting a session. The router pretends to
send "spoof" replies to keepalive messages from the host in an effort to con-
vince the host that the session is up and running. See also: DDR. 2) The
illegal act of sending a packet labeled with a false address, in order to deceive
network security mechanisms such as filters and access lists.

spooler

A management application that processes requests submitted to

it for execution in a sequential fashion from a queue. A good example is a
print spooler.

SPX

Sequenced Packet Exchange: A Novell NetWare transport protocol

that augments the datagram service provided by network layer (Layer 3)
protocols, it was derived from the Switch-to-Switch Protocol of the XNS
protocol suite.

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