Glossary
705
a bit-oriented synchronous Data Link layer protocol created by ISO and
derived from SDLC. However, most HDLC vendor implementations
(including Cisco's) are proprietary. See also: SDLC.
helper address
The unicast address specified, which instructs the Cisco
router to change the client's local broadcast request for a service into a
directed unicast to the server.
hierarchical addressing
Any addressing plan employing a logical chain of
commands to determine location. IP addresses are made up of a hierarchy of
network numbers, subnet numbers, and host numbers to direct packets to
the appropriate destination.
hierarchy
Term used in defining IP addressing; in heirarchical addressing,
some bits are used for networking and some bits for host addressing.
HIP
HSSI Interface Processor: An interface processor used on Cisco 7000
series routers, providing one HSSI port that supports connections to ATM,
SMDS, Frame Relay, or private lines at speeds up to T3 or E3.
holddown
The state a route is placed in so that routers can neither adver-
tise the route nor accept advertisements about it for a defined time period.
Holddown is used to discover bad information about a route from all
routers in the network. A route is generally placed in holddown when one
of its links fails.
hop
The movement of a packet between any two network nodes. See also:
hop count.
hop count
A routing metric that calculates the distance between a
source and a destination. RIP employs hop count as its sole metric. See
also: hop and RIP.
host address
Logical address configured by an administrator or server on
a device. Logically identifies this device on an internetwork.
Host-to-Host layer
Layer in the Internet Protocol suite that is equal to the
Transport layer of the OSI model.
HSCI
High-Speed Communication Interface: Developed by Cisco, a single-
port interface that provides full-duplex synchronous serial communications
capability at speeds up to 52Mbps.
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