EtherWAN EX72129A, User Manual

Page: 137 / 297

137
EtherWAN Managed Switch Users Guide
Path Cost & Port Priority
By default, each port on a Spanning Tree switch will be assigned a Path Cost based on
the port’s transmission speed according to the IEEE standard below:
Link speed Recommended value
Less than or equal 100Kb/s 200,000,000
1 Mb/s 20,000,000
10 Mb/s 2,000,000
100 Mb/s 200,000
1 Gb/s 20,000
10 Gb/s 2,000
100 Gb/s 200
1 Tb/s 20
10 Tb/s 2
By default each port on a Spanning Tree switch will be assigned a Port Priority of
128, according to the IEEE standard. This Port Priority is part of the Port ID, which is
a concatenation of 2 values: Port Priority (4 bits) + Interface ID (12 bits) (see
below )
Figure 53: Port ID
Port Priority is part of the Port ID, which is a concatenation of 2 values: Port Priority
(4 bits) + Interface ID (12 bits).
The default values will work fine in most scenarios; however, there are times when
you may need to adjust these values manually in order to influence the location of
the Alternate Port, the Root Port or the Backup Port.