93• The spanning tree feature is disabled on Device A and Device B and enabled on all devices inuser network 1 and user network 2.• The IRF fabric transparently transmits BPDUs for both user networks and is not involved in thecalculation of spanning trees.When the network topology changes, it takes time for the IRF fabric to update its MAC address tableand ARP table. During this period, traffic in the network might be interrupted.Figure 28 TC Snooping application scenarioTo avoid traffic interruption, you can enable TC Snooping on the IRF fabric. After receiving aTC-BPDU through a port, the IRF fabric updates MAC address table and ARP table entriesassociated with the port's VLAN. In this way, TC Snooping prevents topology change frominterrupting traffic forwarding in the network. For more information about the MAC address table andthe ARP table, see "Configuring the MAC address table" and Layer 3—IP Services ConfigurationGuide.Configuration restrictions and guidelinesWhen you configure TC Snooping, follow these restrictions and guidelines:• TC Snooping and the spanning tree feature are mutually exclusive. You must globally disablethe spanning tree feature before enabling TC Snooping.• The priority of BPDU tunneling is higher than that of TC Snooping. When BPDU tunneling isenabled on a port, the TC Snooping feature does not take effect on the port.• TC Snooping does not support the PVST mode.Configuration procedureTo enable TC Snooping:Step Command Remarks1. Enter system view. system-view N/A2. Globally disable the spanningtree feature.undo stp globalenableBy default, the spanning tree feature isdisabled globally.3. Enable TC Snooping. stp tc-snooping By default, TC Snooping is disabled.
