3Com WX3000 operation manual Configuring Rapid Transition

zWhen the digest snooping feature is enabled on a port, the port state turns to the discarding state. That is, the port will not send BPDU packets. The port is not involved in the STP calculation until it receives BPDU packets from the peer port.

zThe digest snooping feature is needed only when your device is connected to a device of another vendor adopting proprietary spanning tree protocols.

zTo enable the digest snooping feature successfully, you must first enable it on all the ports of your device that are connected to a device of another vendor adopting proprietary spanning tree protocols and then enable it globally.

zTo enable the digest snooping feature, the interconnected devices and the devices of another vendor adopting proprietary spanning tree protocols must be configured with exactly the same MST region-related configurations (including region name, revision level, and VLAN-to-MSTI mapping).

zThe digest snooping feature must be enabled on all the device ports that connect to the devices of other vendors adopting proprietary spanning tree protocols in the same MST region.

zWhen the digest snooping feature is enabled globally, the VLAN-to-MSTI mapping table cannot be modified.

zThe digest snooping feature is not applicable to boundary ports in an MST region.

zThe digest snooping feature is not applicable to edge ports in an MST region.

Configuring Rapid Transition

Introduction

Designated ports of RSTP-enabled or MSTP-enabled devices use the following two types of packets to implement rapid transition:

zProposal packets: Packets sent by designated ports to request rapid transition

zAgreement packets: Packets used to acknowledge rapid transition requests

Both RSTP and MSTP specify that the upstream device can perform rapid transition operation on the designated port only when the port receives an agreement packet from the downstream device. The difference between RSTP and MSTP are:

z

z

For MSTP, the upstream device sends agreement packets to the downstream device; and the downstream device sends agreement packets to the upstream device only after it receives agreement packets from the upstream device.

For RSTP, the upstream device does not send agreement packets to the downstream device.

Figure 1-6 and Figure 1-7 illustrate the rapid transition mechanisms on designated ports in RSTP and MSTP.

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