86 AT-8800 Series Switch User Guide
Software Release 2.6.1
C613-02039-00 REV A
To display the mapping of user priority to QOS egress queues, use the
command:
SHOW SWITCH QOS
Figure 17: Example output from the SHOW SWITCH QOS command
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.
Priority Level QOS egress queue
-------------------------------------
0 ................... 1
1 ................... 0
2 ................... 0
3 ................... 1
4 ................... 2
5 ................... 2
6 ................... 3
7 ................... 3
Table 15: Parameters in the output of the SHOW SWITCH QOS command
Parameter Meaning
Priority level The priority level of the frame.
QOS egress queue The Quality Of Service egress queue that frames with this
priority level join.