Siemens S223 - Manual (Page 205)

User Manual UMN:CLI
SURPASS hiD 6615 S223/S323 R1.5
A50010-Y3-C150-2-7619 205
8.3.2 RSTP 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 B
Switch A
Alternate
Port
Switch C
Switch D
Backup
Port
Path 2 Path 1
ROOT
Designated
Port
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.