3Com Switch 8800 Advanced Software V5 Configuration Guide

128 CHAPTER 11: MSTP CONFIGURATION
Network diagram
Figure 32 Digest Snooping configuration
Configuration procedure
1 Enable Digest Snooping on Switch A
# Enable Digest Snooping on Ethernet 1/1/2.
<SysnameA> system-view
[SysnameA] interface ethernet 1/1/2
[SysnameA-Ethernet1/1/2] stp config-digest-snooping
# Enable global Digest Snooping.
[SysnameA-Ethernet1/1/2] quit
[SysnameA] stp config-digest-snooping
2 Enable Digest Snooping on Switch B (the same as the configuration procedure of
Switch A, omitted)
Configuring No
Agreement Check
Two types of packet are used for rapid state transition on designated RSTP and
MSTP ports:
■ Proposal: Packets sent by designated ports to request rapid transition
■ Agreement: Packets used to acknowledge rapid transition requests
Both RSTP and MSTP switches can perform rapid transition operation on a
designated port only when the port receives an agreement packet from the
downstream switch. The differences between RSTP and MSTP switches are:
■ For MSTP, the downstream device’s root port sends an agreement packet only
after it receives an agreement packet from the upstream device.
■ For RSTP, the down stream device sends an agreement packet regardless of
whether an agreement packet from the upstream device is received.
Figure 33 and Figure 34 show the rapid state transition mechanism on MSTP and
RSTP designated ports.