Allied-telesis AT 8000/8POE User Manual download pdf (Page 157)

AT-S81 Management Software User’s Guide

Section I: Using the Menus Interface 157

Table 8 lists the values. The default value is 0.

If two paths have the same port cost and the same priority, then the ports

with the lowest port MAC addresses become the root ports of their

respective bridges.

Hello Time and Bridge Protocol Data Units (BPDUs)

The bridges that are part of a spanning tree domain communicate with

each other using a bridge broadcast frame that contains a special section

devoted to carrying STP or RSTP information. This portion of the frame is

referred to as the bridge protocol data unit (BPDU). When a bridge is

brought online, it issues a BPDU in order to determine whether a root

bridge has already been selected on the network, and if not, whether it has

the lowest bridge priority number of all the bridges and should therefore

become the root bridge.

The root bridge periodically transmits a BPDU to determine whether there

have been any changes to the network topology and to inform other

bridges of topology changes. The frequency with which the root bridge

sends out a BPDU is called the hello time. This is a value that you can set

in the AT-S81 management software. The interval is measured in seconds

and the default is two seconds. Consequently, if an AT-8000/8POE Fast

Ethernet switch is selected as the root bridge of a spanning tree domain, it

transmits a BPDU every two seconds.

Table 8. Port Priority Value Increments

Port

Priority

Port

Priority

0 128

16 144

32 160

48 176

64 192

80 208

96 224

112 240

1 2 ... 152 153 154 155 156 157 158 159 160 161 162 ... 359 360

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Allied-telesis AT 8000/8POE User Manual Page 157