RSTP priority vector and role selection

Priority vector

Per Bridge

       bridge priority vector = {B:0:B:0:0}

       root priority vector = {B:0:B:0:0}      or

                          = {RD:RPCD+PPCPB:D:PD:PB}

Per Port

       root path priority vector = {RD:RPCD+PPCPB:D:PD:PB}

       designated priority vector = {B:0:B:QB:QB}    or

                            = {RD:RPCD+PPCPB:D:QB:QB}

       port priority vector

Per BPDU

       message priority vector = {RD:RPCD:D:PD:PB}

 

Priority vector update

Port Role Selection state machine

If the message which has been received is aged out on the port, it is set to DesignatedPort (infoIs=Aged)

If the bridge is root or port priority is derived from another port on the bridge, the ports is set to DesignatedPort (infoIs =Mine)

If root priority vector is derived from the port which is set to RootPort (infoIs=Received)

If designated priority vector is higher than port priority vector for the port which is set to DesignatedPort (infoIs=Received)

If designated priority vector is not higher than port priority vector for the port and the designatedBridgeID is this Bridge, then the port is set to BackupPort (infoIs=Received)

If designated priority vector is not higher than port priority vector for the port and the designatedBridgeID is not this Bridge, then the port is set to AlternatePort (infoIs=Received)