tocol (STP). See also: spanning tree and Spanning-Tree
Protocol.
dynamically avoid loops in the network topology by
creating a spanning tree using the spanning-tree algo-
rithm. 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 for-
ward the frames; instead, they're processed to deter-
mine the spanning-tree topology itself. Cisco Catalyst
series switches use STP 802.1d to perform this func-
tion. See also: BPDU, learning bridge, MAC address,
spanning tree, and spanning-tree algorithm.
tree. Sometimes called Dijkstra's algorithm and fre-
quently used in link-state routing algorithms. See also:
link-state routing algorithm.
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 initial-
izes the link to a service provider.
tion about routes is prevented from leaving the router
interface through which that information was
received.
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 ses-
sion. The router pretends to send "spoof" replies to kee-
palive messages from the host in an effort to convince
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 secu-
rity mechanisms such as filters and access lists.
fashion from a queue. A good example is a print
spooler.
service provided by Network layer (Layer 3) proto-
cols, it was derived from the Switch-to-Switch Proto-
col of the XNS protocol suite.
that the collision-detection circuitry is working.
source determines the entire route to a destination
before sending the data and includes that information
in route information fields (RIF) within each packet.
Contrast with: transparent bridging.
transparent bridging. SRT takes advantage of both
technologies in one device, fulfilling the needs of all
end nodes. Translation between bridging protocols is
not necessary. Compare with: SR/TLB.
communicate with transparent bridge stations aided
by an intermediate bridge that translates between the
two bridge protocols. Used for bridging between
Token Ring and Ethernet. Compare with: SRT.
packet. See also: DSAP and SAP.
coded into the Silicon Switch Processor (SSP). Silicon
switching is available only on the Cisco 7000 with an
SSP. Silicon-switched packets are compared to the sil-
icon-switching cache on the SSE. The SSP is a dedi-
cated switch processor that offloads the switching
process from the route processor, providing a fast-
switching solution, but packets must still traverse the
backplane of the router to get to the SSP and then back
to the exit interface.