Open System Services NFS SCF Reference Manual

Glossary
Open System Services NFS SCF Reference Manual—522582-001
Glossary-6
hierarchical routing
hierarchical routing. Routing based on a hierarchical addressing scheme. Most Internet
routing is based on a two-level hierarchy in which an Internet address is divided into a
network portion and a host portion. Gateways use only the network portion until the
datagram reaches a gateway that can deliver it directly. Subnetworking introduces
additional levels of hierarchical routing.
hop count. A measure of distance between two points in the Internet. A hop count of n
means that n gateways separate the source and destination.
ICMP. See Internet Control Message Protocol (ICMP)
.
IGP. See Interior Gateway Protocol (IGP)
.
Interior Gateway Protocol (IGP). The generic term applied to any protocol used to
propagate network reachability and routing information within an autonomous system.
Although no standard Internet IGP exists, Routing Information Protocol (RIP) is among
the most popular.
Internet. The collection of networks and gateways, including the ARPANET, MILNET, and
NSF network, that use the Transmission Control Protocol/Internet Protocol (TCP/IP)
suite and function as a single, cooperative virtual network. The Internet provides
universal connectivity and three levels of network service: unreliable, connectionless
packet delivery; reliable, full-duplex stream delivery; and application-level services like
electronic mail that build on the first two.
Internet address. The 32-bit address assigned to hosts that want to participate in the Internet
using Transmission Control Protocol/Internet Protocol (TCP/IP). Internet addresses are
the abstraction of physical hardware addresses, just as the Internet is an abstraction of
physical networks. Actually assigned to the interconnection of a host to a physical
network, an Internet address consists of a network portion and a host portion. This
partition makes routing efficient.
Internet Control Message Protocol (ICMP). An integral part of the Internet Protocol (IP)
that handles error and control messages. Specifically, gateways and hosts use ICMP to
send reports of problems about datagrams back to the original source that sent the
datagram. ICMP also includes an echo request/reply used to test whether a destination is
reachable and responding. This protocol is used by the network layer to communicate
the reachability of particular network nodes as well as routing control information.
ICMP is part of IP because it shares the same Ethernet type field.
Internet Protocol (IP). The Internet-standard protocol that defines the Internet datagram as
the unit of information passed across the Internet, and that provides the basis for the
Internet connectionless, best-effort packet-delivery service.
interoperability. (1) Within a Himalaya node, the ability to use the features or facilities of
one environment from another. For example, the gtacl command in the OSS
environment allows an interactive user to start and use a Guardian tool in the Guardian
environment.
(2) Among systems from multiple vendors or with multiple versions of operating
systems from the same vendor, the ability to exchange status, files, and other