NBT Manual

Glossary
NBT Manual—424773-001
Glossary-2
autonomous system
autonomous system. A collection of gateways and networks that fall under one
administrative entity and cooperate closely to propagate network reachability (and
routing) information among themselves using an interior gateway protocol of their
choice. Gateways within an autonomous system have a high degree of trust. At least one
gateway in an autonomous system must advertise networks in that system to a core
gateway using EGP.
baseband. Characteristic of any network technology (like Ethernet) that uses a single carrier
frequency and requires all stations attached to the network to participate in every
transmission. See broadband
.
bridge. A router that connects two or more networks and forwards packets among them.
Usually, bridges operate at the physical network level. For example, an Ethernet bridge
connects two physical Ethernet cables and forwards from one cable to the other exactly
those packets that are not local. Bridges differ from repeaters; bridges store and forward
complete packets, while repeaters forward electrical signals.
broadband. Characteristic of any network technology that multiplexes multiple, independent
network carriers onto a single cable (usually using frequency division multiplexing). For
example, a single 100 mbps broadband cable can be divided into ten 10 mbps carriers,
with each treated as an independent Ethernet. The advantage of broadband is less cable;
the disadvantage is higher cost for equipment. See baseband
.
broadcast. A packet delivery system that delivers a copy of a given packet to all hosts that
attach to it is said to broadcast the packet. Broadcast may be implemented with hardware
or software.
BSD. Berkeley Software Distribution.
Class A. The network number is 1 through 127 (1 octet); that is, the first octet is in the range
1-127. The remaining three octets in the address are used for the subnet number and host
number.
Class B. The network number is 128 through 191.255 (2 octets); that is, the first octet is in
the range 128-191, the second octet is in the range 0-255. The remaining two octets are
used for the subnet number and host number.
Class C. The network number is 192.0.0 through 255.255.255 (3 octets); that is, the first octet
is in the range 192-255, the second octet is in the range 0-255, and the third octet is in
the range 0-255. The remaining octet is used for the subnet number and host number.
The subnet number varies in length. The subnet number's width is typically represented
by a bit mask. The rest of the available bits uniquely identify the host connected to the
subnetwork. LANs connected by way of a gateway to the INTERNET get their subnet
class from the DCA's NIC (Network Information Center). The address classes of
standalone, or entirely private, LANs are administered by the LAN administrator.
Typical usage calls for all CLASS A addresses to have private LANs.