valutazioni - 4, GPA: 3.5 ( )

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This creates one spanning tree instance for the entire network. If multiple VLANs are implemented on a network, the path between specific VLAN members may be inadvertently disabled to prevent network loops, thus isolating group members. When operating multiple VLANs, we recommend selecting the MSTP option. • Rapid Spanning Tree Protocol RSTP supports connections to either STP or RSTP nodes by monitoring the incoming protocol messages and dynamically adjusting the type of protocol messages the RSTP node transmits, as described below: - STP Mode - If the switch receives an 802.1D BPDU (i.e., STP BPDU) after a port's migration delay timer expires, the switch assumes it is connected to an 802.1D bridge and starts using only 802.1D BPDUs. - RSTP Mode - If RSTP is using 802.1D BPDUs on a port and receives an RSTP BPDU after the migration delay expires, RSTP restarts the migration delay timer and begins using RSTP BPDUs on that port. 3-95 ^3 Configuring the Switch • Multiple Spanning Tree Protocol - To allow multiple spanning trees to operate over the network, you must configure a related set of bridges with the same MSTP configuration, allowing them to participate in a specific set of spanning tree instances. - A spanning tree instance can exist only on bridges that have compatible VLAN instance assignments. - Be careful when switching between spanning tree modes. Changing modes stops all spanning-tree instances for the previous mode and restarts the system in the new mode, temporarily disrupting user traffic. Command Attributes Basic Configuration of Global Settings • Spanning Tree State - Enables/disables STA on this switch. (Default: Enabled) • Spanning Tree Type - Specifies the type of spanning tree used on this switch: - STP: Spanning Tree Protocol (IEEE 802.1D); i.e., when this option is selected, the switch will use RSTP set to STP forced compatibility mode). - RSTP: Rapid Spanning Tree (IEEE 802.1w) - MSTP: Multiple Spanning Tree (IEEE 802.1s); MSTP is the default. • 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. (Note that lower numeric values indicate higher priority.) • Default: 32768 • Range: 0-61440, in steps of 4096 • Options: 0, 4096, 8192, 12288, 16384, 20480, 24576, 28672, 32768, 36864, 40960, 45056, 49152, 53248, 57344, 61440 Root Device Configuration • Hello Time - Interval (in seconds) at which the root device transmits a configuration message. • Default: 2 • Minimum: 1 • Maximum: The lower of 10 or [(Max. Message Age / 2) -1] • Maximum 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.) • Default: 20 • Minimum: The higher of 6 or [2 x (Hello Time + 1)]. • Maximum: The lower of 40 or [2 x (Forward Delay - 1)] 3-96 Spanning Tree Algorithm Configuration • 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 information that would make it return to a discarding state; otherwise, temporary data loops might result. • Default: 15 • Minimum: The higher of 4 or [(Max. Message Age / 2) + 1] • Maximum: 30 Configuration Settings for RSTP The following attributes apply to both RSTP and MSTP: • Path Cost Method - The path cost is used to determine the best path between devices. The path cost method is used to determine the range of values that can be assigned to each interface. • Long: Specifies 32-bit based values that range from 1-200,000,000. (This is the default.) • Short: Specifies 16-bit based values that range from 1-65535. • Transmission Limit - The maximum transmission rate for BPDUs is specified by setting the minimum interval between the transmission of consecutive protocol messages. (Range: 1-10; Default: 3) Configuration Settings for MSTP • Max Instance Numbers - The maximum number of MSTP instances to which this switch can be assigned. (Default: 65) • Configuration Digest - An MD5 signature key that contains the VLAN ID to MST ID mapping table. In other words, this key is a mapping of all VLANs to the CIST. • Region Revision* - The revisi...

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