Allied Telesis 2.6.1 manual Spanning Tree Protocol STP, Spanning Tree Modes

86 AT-8800 Series Switch User Guide

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

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.

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.

Software Release 2.6.1 C613-02039-00 REV A