Allied Telesis Rapier i AT-RP16Fi/SC, User Manual

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Layer 2 Switching 89
Software Release 2.6.1
C613-02025-00 REV C
Spanning Tree Protocol (STP)
The Spanning Tree Protocol (STP) makes it possible to automatically disable
redundant paths in a network to avoid loops, and enable them when a fault in
the network means they are needed to keep traffic flowing. A sequence of
LANs and switches may be connected together in an arbitrary physical
topology resulting in more than one path between any two switches. If a loop
exists, frames transmitted onto the extended LAN would circulate around the
loop indefinitely, decreasing the performance of the extended LAN. On the
other hand, multiple paths through the extended LAN provide the opportunity
for redundancy and backup in the event of a bridge experiencing a fatal error
condition.
The spanning tree algorithm ensures that the extended LAN contains no loops
and that all LANs are connected by:
■
Detecting the presence of loops and automatically computing a logical
loop-free portion of the topology, called a
spanning tree . The topology is
dynamically pruned to a spanning tree by declaring the ports on a switch
redundant, and placing the ports into a ‘Blocking’ state.
■
Automatically recovering from a switch failure that would partition the
extended LAN by reconfiguring the spanning tree to use redundant paths,
if available.
Spanning Tree Modes
STP can run in STANDARD mode, or RAPID mode. Rapid mode allows for
rapid configuration of the spanning tree. The Rapid Spanning Tree Protocol
(RSTP) is specified in IEEE 802.1w.
Hardware packet filters Priority queueing of classified traffic flows.
Replacing TOS or DSCP byte of IP header.
Replacing User Priority in VLAN tag header.
Forwarding a flow that is marked to be dropped (for
example, because bandwidth allocation is exceeded).
Specifying actions for packets which match the ingress
and egress ports of a classifier (if set), but do not match
the classifier’s other parameters.
Configuring a simple DiffServ domain.
Bandwidth limiting.
Configuring most DiffServ domains.
Layer 3 switch filters Priority queueing of up to 16 distinctly different types
of traffic flow.
Replacing TOS or DSCP byte of IP header.
Replacing User Priority in VLAN tag header.
QoS for non-IP traffic (e.g. IPX).
QoS based on VLANs.
Bandwidth limiting.
SET SWITCH PORT Limiting total ingress and/or egress bandwidth on
ports. Limiting bandwidth of particular types of
traffic.
Limiting egress bandwidth if priority
queueing is also required.
Table 15: The different QoS-type controls available on the switch.
Command set Use for Do not use for