Siemens S223, S323 user manual Mstp Operation, Compatibility with 802.1d

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

It is same with 802.1d to block the connection of SWITCH D and SWITCH C. However, 802.1w does not need any configured time to negotiate between switches to make for- warding state of specific port. So it is very fast progressed. During progress to forwarding state of port, listening and learning are not needed. These negotiations use BPDU.

Compatibility with 802.1d

RSTP internally includes STP, so it has compatibility with 802.1d. Therefore, RSTP can recognize BPDU of STP. But, STP cannot recognize BPDU of RSTP. For example, as- sume that SWITCH A and SWITCH B are operated as RSTP and SWITCH A is connected to SWITCH C as designated switch. Since SWITCH C, which is 802.1d ignores RSTP BPDU, it is interpreted that switch C is not connected to any switch or segment.

Switch A	Switch B	Switch C
(802.1w)	(802.1w)	(802.1d)

RSTP BPDU STP BPDU

Fig. 8.20 Compatibility with 802.1d (1)

However, SWITCH A converts a port received BPDU into RSTP of 802.1d because it can read BPDU of SWITCH C. Then SWITCH C can read BPDU of SWITCH A and accepts SWITCH A as designated switch.

Switch A	Switch B	Switch C
(802.1w)	(802.1w)	(802.1d)

STP BPDU

Fig. 8.21 Compatibility with 802.1d (2)

8.3.3MSTP Operation

To operate the network more effectively, the hiD 6615 S223/S323 uses MSTP (Multiple Spanning-Tree Protocol). It constitutes the network with VLAN subdividing existing LAN domain logically and configure the route by VLAN or VLAN group instead of existing rout- ing protocol.

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