Hirschmann MACH 1000, Reference Manual

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Glossary
545
CLI L2P
Release 7.0 05/2011
8 Glossary
Numerics
802.1D. The IEEE designator for
Spanning Tree Protocol (STP). STP,
a link management protocol, is part
of the 802.1D standard for media
access control bridges. Using the
spanning tree algorithm, STP
provides path redundancy while
preventing endless loops in a
network. An endless loop is created
by multiple active paths between
stations where there are alternate
routes between hosts. To establish
path redundancy, STP creates a
logical tree that spans all of the
switches in an extended network,
forcing redundant paths into a
standby, or blocked, state. STP
allows only one active path at a time
between any two network devices
(this prevents the loops) but
establishes the redundant links as a
backup if the initial link should fail. If
STP costs change, or if one network
segment in the STP becomes
unreachable, the spanning tree
algorithm reconfigures the spanning
tree topology and reestablishes the
link by activating the standby path.
Without spanning tree in place, it is
possible that both connections may
be simultaneously live, which could
result in an endless loop of traffic on
the LAN.
802.1P. The IEEE protocol
designator for Local Area Network
(LAN). This Layer 2 network
standard improves support of time
critical traffic, and limits the extent of
high bandwidth multicast traffic
within a bridged LAN. To do this,
802.1P defines a methodology for
introducing traffic class priorities.
The 802.1P standard allows priority
to be defined in all 802 MAC
protocols (Ethernet, Token Bus,
Token Ring), as well as in FDDI. For
protocols (such as Ethernet) that do
not contain a priority field, 802.1P
specifies a method for indicating
frame priority based on the new
fields defined in the 802.1Q (VLAN)
standard.
802.1Q VLAN. The IEEE protocol
designator for Virtual Local Area
Network (VLAN). This standard
provides VLAN identification and
quality of service (QoS) levels. Four
bytes are added to an Ethernet
frame to allow eight priority levels
(QoS) and to identify up to 4096
VLANs. See “VLAN” on page 558 for
more information.
A
Address Resolution Protocol. An
Internet Protocol that dynamically
maps Internet addresses to physical
(hardware) addresses on a LAN.