The Bridge Parameters - Hirschmann PowerMICE User Manual

Rapid Spanning Tree

1.1.2 The bridge parameters

Each bridge is uniquely described by the following parameters:
D
Bridge Identifier,
D
Root path costs of the bridge ports
D
Port Identifier.
Bridge Identifier
U
The bridge identifier is 8 bytes long. The two highest-value bytes are the
priority number. The default setting for the priority number is 32 768, but
the Management Administrator can change this when configuring the
network. The six lowest-value bytes of the bridge identification are the
MAC address of the bridge. The MAC address guarantees that every
bridge has a different bridge identification.
The bridge with the numerically lowest-value bridge identifier has the
highest priority.
MSB
Priority
Fig. 1: Bridge identifier
Root path costs
U
Each path connecting two bridges has transmission costs assigned to it.
The management administrator sets this value and specifies it for each
path when configuring a bridge (see Table 2 on page 16). It assigns the
higher path costs to paths with lower transmission speeds.
Alternatively, the Management Administrator can define the path costs.
Like the switch, it assigns the higher path costs to paths with lower trans-
mission speeds. Because he essentially has a free hand in specifying
this value, he has a tool for ensuring that in case of redundant paths one
path will be favored over the others.
The root path costs are calculated by adding up the individual path costs
Redundancy L3P
Release 3.0 01/07
1.1 The Spanning Tree Protocol
MAC Address
LSB
15