Hirschmann RS20 Reference Manual page 221

Glossary
direct protocol used to communicate
datagrams over a network with little
error recovery) and provides no
security features. It is often used by
servers to boot diskless
workstations, X-terminals, and
routers.
Trunking. The process of combing
a set of trunks that are traffic-
engineered as a unit for the
establishment of connections
between switching systems in which
all of the communications paths are
interchangeable.
U
UPM. User Programmable
Machine.
UPMA. The first of two UPMs in
Motorola's MPC855T processor.
UPMB. The second of two UPMs in
Motorola's MPC855T processor.
USP. An abbreviation that
represents Unit, Slot, Port.
V
Virtual Local Area Network.
Operating at the Data Link Layer
(Layer 2 of the OSI model), the
VLAN is a means of parsing a single
network into logical user groups or
organizations, as if they physically
resided on a dedicated LAN
segment of their own. In reality, this
virtually defined community may
have individual members peppered
221
across a large, extended LAN. The
VLAN identifier is part of the 802.1Q
tag, which is added to an Ethernet
frame by an 802.1Q-compliant
switch or router. Devices
recognizing 802.1Q-tagged frames
maintain appropriate tables to track
VLANs. The first three bits of the
802.1Q tag are used by 802.1P to
establish priority for the packet.
Virtual Router Redundancy
Protocol. VRRP specifies an
election protocol that dynamically
assigns responsibility for a virtual
router to one of the VRRP routers on
a LAN. The VRRP router controlling
the IP address(es) associated with a
virtual router is called the Master,
and forwards packets sent to these
IP addresses. The election process
provides dynamic fail-over in the
forwarding responsibility should the
Master become unavailable. This
allows any of the virtual router IP
addresses on the LAN to be used as
the default first hop router by end-
hosts. The advantage gained from
using VRRP is a higher availability
default path without requiring
configuration of dynamic routing or
router discovery protocols on every
end-host.
VLAN. See "Virtual Local Area
Network" on page 221.
vMAN. Virtual Metropolitan Area
Network.
VRRP. See "Virtual Router
Redundancy Protocol" on page 221.
CLI L2B
Release 4.0 11/07