Extreme Networks ExtremeWare XOS Guide Manual page 471

S (continued)
STP
STPD
STPD mode
stub areas
system health check
T
TACACS+
tagged VLAN
ExtremeWare XOS 11.1 Concepts Guide
Spanning Tree Protocol. STP is a protocol, defined in IEEE 802.1d,
used to eliminate redundant data paths and to increase network
efficiency. STP allows a network to have a topology that contains
physical loops; it operates in bridges and switches. STP opens certain
paths to create a tree topology, thereby preventing packets from
looping endlessly on the network. To establish path redundancy, STP
creates a 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 STP topology and re-establishes the link by activating
the standby path.
Spanning Tree Domain. An STPD is an STP instance that contains one
or more VLANs. The switch can run multiple STPDs, and each STPD
has its own root bridge and active path. In the Extreme Networks
implementation of STPD, each domain has a carrier VLAN (for
carrying STP information) and one or more protected VLANs (for
carrying the data).
The mode of operation for the STPD. The two modes of operation are:
802.1d—Compatible with legacy STP and other devices using the
●
IEEE 802.1d standard.
802.1w—Compatible with Rapid Spanning Tree (RSTP).
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In OSPF, a stub area is connected to only one other area (which can be
the backbone area). External route information is not distributed to
stub areas.
The primary responsibility of the system health checker is to monitor
and poll error registers. In addition, the system health checker can be
enabled to periodically send diagnostic packets. System health check
errors are reported to the syslog.
Terminal Access Controller Access Control System. Often run on UNIX
systems, the TACAS+ protocol provides access control for routers,
network access servers, and other networked computing devices via
one or more centralized servers. TACACS+ provides separate
authentication, authorization, and accounting services. User passwords
are administered in a central database rather than in individual
routers, providing easily scalable network security solutions.
You identify packets as belonging to the same tagged VLAN by
putting a value into the 12-bit (4 octet) VLAN ID field that is part of
the IEEE 802.1Q field of the header. Using this 12-bit field, you can
configure up to 4096 individual VLAN addresses (usually some are
reserved for system VLANs such as management and default VLANs);
these tagged VLANs can exist across multiple devices. The tagged
VLAN can be associated with both tagged and untagged ports.
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