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Фрагмент инструкции
Frequent changes in the tree structure can easily isolate some of the group members. MSTP (an extension of RSTP) is designed to support independent spanning trees based on VLAN groups. Once you specify the VLANs to include in a Multiple Spanning Tree Instance (MSTI), the protocol will automatically build an MSTI tree to maintain connectivity among each of the VLANs. MSTP maintains contact with the global network because each instance is treated as an RSTP node in the Common Spanning Tree (CST). Displaying Global Settings You can display a summary of the current bridge STA information that applies to the entire switch using the STA Information screen. Field Attributes • Spanning Tree State - Shows if the switch is enabled to participate in an STA-compliant network. • Bridge ID - A unique identifier for this bridge, consisting of the bridge priority and MAC address (where the address is taken from the switch system). • Max Age - The maximum time (in seconds) a device can wait without receiving a configuration message before attempting to reconfigure. All device ports (except for designated ports) should receive configuration messages at regular intervals. Any port that ages out STA information (provided in the last configuration message) becomes the designated port for the attached LAN. If it is a root port, a new root port is selected from among the device ports attached to the network. (References to “ports” in this section mean “interfaces,” which includes both ports and trunks.) 3-92 Spanning Tree Algorithm Configuration • Hello Time - Interval (in seconds) at which the root device transmits a configuration message. • Forward Delay - The maximum time (in seconds) the root device will wait before changing states (i.e., discarding to learning to forwarding). This delay is required because every device must receive information about topology changes before it starts to forward frames. In addition, each port needs time to listen for conflicting information that would make it return to a discarding state; otherwise, temporary data loops might result. • Designated Root - The priority and MAC address of the device in the Spanning Tree that this switch has accepted as the root device. • Root Port - The number of the port on this switch that is closest to the root. This switch communicates with the root device through this port. If there is no root port, then this switch has been accepted as the root device of the Spanning Tree network. • Root Path Cost - The path cost from the root port on this switch to the root device. • Configuration Changes - The number of times the Spanning Tree has been reconfigured. • Last Topology Change - Time since the Spanning Tree was last reconfigured. These additional parameters are only displayed for the CLI: • Spanning tree mode - Specifies the type of spanning tree used on this switch: - STP: Spanning Tree Protocol (IEEE 802.1 D) - RSTP: Rapid Spanning Tree (IEEE 802.1w) - MSTP: Multiple Spanning Tree (IEEE 802.1s) • Instance - Instance identifier of this spanning tree. (This is always 0 for the CIST.) • Vlans configuration - VLANs assigned to the CIST. • Priority - Bridge priority is used in selecting the root device, root port, and designated port. The device with the highest priority becomes the STA root device. However, if all devices have the same priority, the device with the lowest MAC address will then become the root device. • Root Hello Time - Interval (in seconds) at which this device transmits a configuration message. • Root Maximum Age - The maximum time (in seconds) this device can wait without receiving a configuration message before attempting to reconfigure. All device ports (except for designated ports) should receive configuration messages at regular intervals. If the root port ages out STA information (provided in the last configuration message), a new root port is selected from among the device ports attached to the network. (References to “ports” in this section means “interfaces,” which includes both ports and trunks.) • Root Forward Delay - The maximum time (in seconds) this device will wait before changing states (i.e., discarding to learning to forwarding). This delay is required because every device must receive information about topology changes before it starts to forward frames. In addition, each port needs time to listen for conflicting 3-93 ^3 Configuring the Switch information that would make it return to a discarding state; otherwise, temporary data loops might result. • Root Hold Time - The interval (in seconds) during which no more than two bridge configuration protocol data units shall be transmitted by this node. • Max hops - The max number of hop counts for the MST region. • Remaining hops - The remaining number of hop counts for the MST instance. • Transmission limit - The minimum interval between the transmission of consecutive RSTP/MSTP BPDUs. • Path Cost Method - The path cost is used to determine the be...
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