71In addition to basic MSTP features, the following features are provided for ease of management:• Root bridge hold• Root bridge backup• Root guard• BPDU guard• Loop guard• TC-BPDU guard• Port role restriction• TC-BPDU transmission restriction• Support for hot swapping of interface cards and active/standby changeover.Protocols and standardsMSTP is documented in the following protocols and standards:• IEEE 802.1d, Media Access Control (MAC) Bridges• IEEE 802.1w, Part 3: Media Access Control (MAC) Bridges—Amendment 2: RapidReconfiguration• IEEE 802.1s, Virtual Bridged Local Area Networks—Amendment 3: Multiple Spanning Trees• IEEE 802.1Q-REV/D1.3, Media Access Control (MAC) Bridges and Virtual Bridged Local AreaNetworks —Clause 13: Spanning tree ProtocolsGeneral configuration restrictions and guidelines• In an IRF 3 system, a device in PVST mode can maintain a maximum of 254 spanning trees. Ifa PVST device is not in an IRF 3 system, it can maintain a maximum of 510 spanning trees.• If both MVRP and spanning tree are enabled on a network, MVRP packets are forwarded alongMSTIs. To advertise a specific VLAN within the network through MVRP, make sure this VLAN ismapped to an MSTI when you configure the VLAN-to-instance mapping table. For moreinformation about MVRP, see "Configuring MVRP."• To connect a spanning tree network to a TRILL network, make sure the following requirementsare met:{ The spanning tree protocol is disabled on the TRILL network.{ An edge port is used to connect the spanning tree network to the TRILL network. The edgeport can quickly transit to the forwarding state. This prevents network topology changesfrom influencing the TRILL network.For more information about TRILL, see TRILL Configuration Guide.• The spanning tree configurations are mutually exclusive with service loopback, RRPP, andSmart Link on a port.• Configurations made in system view take effect globally. Configurations made in Ethernetinterface view take effect only on the interface. Configurations made in Layer 2 aggregateinterface view take effect only on the aggregate interface. Configurations made on anaggregation member port can take effect only after the port is removed from the aggregationgroup.• After you enable a spanning tree protocol on a Layer 2 aggregate interface, the systemperforms spanning tree calculation only on the Layer 2 aggregate interface. It does not performspanning tree calculation on the aggregation member ports. The spanning tree protocol stateand forwarding state of each selected member port are consistent with those of thecorresponding Layer 2 aggregate interface.
