
220 Glossary
ICMP Internet Control Message Protocol. A message control and error-reporting
protocol used between host servers and gateways. For example, some Internet
software applications use ICMP to send a packet on a round-trip between two hosts to
determine round-trip times and discover problems on the network.
idle user A user who is connected to the server but hasn’t used the server volume for a
period of time.
IGMP Internet Group Management Protocol. An Internet protocol used by hosts and
routers to send packets to lists of hosts that want to participate in a process known as
multicasting. QuickTime Streaming Server (QTSS) uses multicast addressing, as does
Service Location Protocol (SLP).
IMAP Internet Message Access Protocol. A client-server mail protocol that allows users
to store their mail on the mail server rather than download it to the local computer.
Mail remains on the server until the user deletes it.
IP Internet Protocol. Also known as IPv4. A method used with Transmission Control
Protocol (TCP) to send data between computers over a local network or the Internet. IP
delivers packets of data, while TCP keeps track of data packets.
IP subnet A portion of an IP network, which may be a physically independent network
segment, that shares a network address with other portions of the network and is
identified by a subnet number.
ISP Internet service provider. A business that sells Internet access and often provides
web hosting for ecommerce applications as well as mail services.
Kerberos A secure network authentication system. Kerberos uses tickets, which are
issued for a specific user, service, and period of time. Once a user is authenticated, it’s
possible to access additional services without retyping a password (this is called single
sign-on) for services that have been configured to take Kerberos tickets. Mac OS X
Server uses Kerberos v5.
Kerberos realm The authentication domain comprising the users and services that are
registered with the same Kerberos server. The registered services and users trust the
Kerberos server to verify each other’s identities.
LDAP Lightweight Directory Access Protocol. A standard client-server protocol for
accessing a directory domain.
lease period A limited period of time during which IP addresses are assigned. By using
short leases, DHCP can reassign IP addresses on networks that have more computers
than available IP addresses.
load balancing The process of distributing client computers’ requests for network
services across multiple servers to optimize performance.
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