Introduction
1-4 Useful Definitions
Therefore, a site’s core gateway must have routing information on all networks
available within the autonomous site, and must be able to pass reachability (of
other Internet sites) information (using EGP) to each network gateway in that site.
Flags
The control bits indicating special functions for a TCP segment; for example, if the
datagram is allowed to be fragmented, and if so, whether other later fragments
exist.
Fragment
An IP datagram containing only a portion of the user-data from a larger IP
datagram. A datagram will be fragmented if its size is too large to be encapsulated
within the legal limits of a frame’s data field of the medium on which it is
transmitted (e.g., a datagram over 1500 bytes would be fragmented if it were to be
transmitted on an Ethernet network).
Fragmentation
The process of breaking an IP datagram into smaller parts, such that each
fragment can be transmitted in whole on a given physical medium.
Gateway
A router (for the purposes of this manual).
Internet
A large collection of connected networks, primarily in the United States, running
the Internet suite of protocols, also known as the DARPA Internet.
Internet Control Message Protocol (ICMP)
A simple protocol that provides low-level feedback that informs the internet layer
about its operating status. Control messages supported by this protocol include
destination unreachable; datagram discards because of timer expirations; IP
header problems; discards at a destination because of a lack of resources; redirects
to a gateway closer than the device’s default one; IP address reachability tests and
results; delay times between transmission and reception of datagrams; and IP
network address and address mask requests.
Internet Protocol (IP)
The network protocol offering a connectionless mode network service in the
Internet Suite of protocols, in which address resolution and data transfer are
completed in a single phase.
Management Information Base (MIB)
A collection of objects (organized in accordance with the Structure of
Management Information) implemented in a network device, so that the device
can be accessed and managed by a network management protocol, such as SNMP.
Objects allow a device to be monitored (have information retrieved from it by a
management station); to be controlled (allow remote configuration of the device,
such as switching the operational state of a port); and to report abnormal events
to the management station (e.g., collision threshold exceeded).