SMC Networks 7724M/VSW - annexe 1, Руководство пользователя

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Management Guide CLI
TigerAccess™ EE
SMC7824M/VSW 259
It is named as BPDU (Bridge Protocol Data Unit). Switches decide port state based on
the exchanged BPDU and automatically decide an optimized path to communicate with
the root switch.
Root Switch
The critical information to decide a root switch is the bridge ID. Bridge ID is composed of
two bytes-priority and six bytes-MAC address. The root switch is decided with the lowest
bridge ID.
Switch B
Switch A
Priority : 9
Switch C
Switch D
Priority : 10
Priority : 8
ROOT
DP
DP
RP RP
DP
DP
RP
RP = Root Port
DP = Designated Port
Fig. 8.11 Root Switch
After configuring STP, switches exchange their information. The priority of SWITCH A is 8,
the priority of SWITCH B is 9 and the priority of SWITCH C is 10. In this case, SWITCH A
is automatically configured as root switch.
Designated Switch
After deciding a root switch, when SWITCH A transmits packet to SWITCH C, SWITCH A
compares the exchanged BPDU to decide a path. The critical information to decide path
is path-cost. Path-cost depends on the transmit rate of LAN interface and path with lower
path-cost is selected.
The standard to decide a designated switch is total root path-cost which is added with
path-cost to the root switch. Path-cost depends on transmit rate of switch LAN interface
and switch with lower path-cost is selected to be a designated switch.