Siemens S323, S223 user manual Bpdu Policy, Rapid Network Convergence

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

BPDU Policy

802.1d forwards BPDU following Hello-time installed in root switch and the other switch except root switch its own BPDU only when receiving BPDU from root switch. However, in 802.1w not only root switch but also all the other switches forward BPDU following Hello- time. BPDU is more frequently changed than the interval root switch exchanges, but with 802.1w it becomes faster to be master of the situation of changing network.

By the way, when low BPDU is received from root switch or designated switch, it is im- mediately accepted. For example, suppose that root switch is disconnected to SWITCH B. Then, SWITCH B is considered to be root because of the disconnection and forwards BPDU.

However, SWITCH C recognizes root existing, so it transmits BPDU including information of root to Bridge B. Thus, SWITCH B configures a port connected to SWITCH C as new root port.

Switch A

ROOT

New Root

Port

Switch B Low BPDU Switch C

BPDU including

Root information

Fig. 8.15 Example of Receiving Low BPDU

Rapid Network Convergence

A new link is connected between SWITCH A and root. Root and SWITCH A is not directly connected, but indirectly through SWITCH D. After SWITCH A is newly connected to root, packet cannot be transmitted between the ports because state of two switches becomes listening, and no loop is created.

In this state, if root transmits BPDU to SWITCH A, SWITCH A transmits new BPDU to SWITCH A and SWITCH C, switch C transmits new BPDU to SWITCH D. SWITCH D, which received BPDU from SWITCH C makes port connected to SWITCH C Blocking state to prevent loop after new link.

206 A50010-Y3-C150-2-7619