Siemens S223, S323 user manual Rstp Operation, Switch B Switch C, Backup, Port Path Switch D

User Manual	UMN:CLI
SURPASS hiD 6615 S223/S323 R1.5

8.3.2RSTP Operation

STP or RSTP is configured on network where Loop can be created. However, RSTP is more rapidly progressed than STP at the stage of reaching to the last topology. This sec- tion describes how the RSTP more improved than STP works. It contains the below sec- tions.

•Port States

•BPDU Policy

•Rapid Network Convergence

•Compatibility with 802.1d.

Port States

RSTP defines port states as discarding, learning, and forwarding. Blocking of 802.1d and listening is combined into discarding. Same as STP, root port and designated port are de- cided by port state. But a port in blocking state is divided into alternate port and backup port. Alternate port means a port blocking BPDUs of priority of high numerical value from other switches, and backup port means a port blocking BPDUs of priority of high numeri- cal value from another port of same equipment.

Switch A

ROOT

Switch B			Switch C
Alternate	Designated		Backup
Port		Port	Port
	Path 1	Path 2

Switch D

Fig. 8.14 Alternate Port and Backup port

The difference of between alternate port and backup port is that alternate port can alter- nate path of packet when there is a problem between Root switch and SWITCH C but Backup port cannot provide stable connection in that case.

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