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7000 Series L3 Managed Switch Reference Manual for Software v1.0
C-24 Glossary
May 30, 2003 Beta Draft
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.
UTP
Unshielded twisted pair is the cable used by 10BASE-T and 100BASE-Tx Ethernet networks.
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 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.