Network Element-Level Management Help >>Protocol Management >> Port MSTP Configuration

Port MSTP Configuration

Operation Procedure

1. Select the Resource tab.
2. Select the device to be managed from the device list to enter the Device Details page.
3. Click MSTP Management in the protocol management list.
4. Click the Port MSTP tab of the MSTP Management page.

Parameter Description

• Priority: The priority of a port is an important factor in determining whether the port can be elected as the root port of a device during the spanning tree calculation process. If all other conditions are the same, the port with the highest priority will be elected as the root port. On an MSTP-enabled device, a port can have different priorities in different MSTIs, and the same port can play different roles in different MSTIs, so that data of different VLANs can be propagated along different physical paths, thus implementing per-VLAN load balancing. When the priority of a port is changed, MSTP will re-compute the role of the port and initiate a state transition. Generally, a configured lower priority value indicates a higher priority of the port. If all the ports of a switch have the same port priority value, the port priorities are determined by the port indexes. Changing the priority of an Ethernet port triggers a new spanning tree computing process. You can set port priority values based on the actual networking requirements. The default port priority is 128.
• Path Cost to Root Bridge: Parameter related to the rate of port-connected links. On a switch supporting MSTP, the port may have varying path costs in different spanning tree instances so that traffic of different VLANs can be forwarded along different physical links to implement per-VLAN load sharing. By default, MSTP calculates the path cost of each port.
• CIST Edge Port: It is only applicable to the case when the MSTI is a CIST. Edge port means that the port is neither directly connected to any switch nor indirectly connected to any switch through the port-connected network. When the user specifies one port as the edge port and when the port migrates from the congestion state to forwarding state, the fast migration can be implemented without any delay. The user can only configure the port connecting the terminal as the edge port. If BPDUs from other port are received on the edge port, the port will become a non-edge port again. The parameter is valid for all spanning tree instances, meaning that when the port is configured as an edge port or non-edge port, the port is configured as an edge port or non-edge port on the CIST and all MSTIs. When the port receives BPDUs, the port actually operates as a non-edge port even it is configured as the edge port by the user. By default, all Ethernet ports of a switch are non-edge ports.
• CIST Port Point-to-Point: Point-to-Point link generally refers to the link between switches. The two ports in a point-to-point link can be quickly migrated to forwarding state by transmitting the synchronous packets, thus reducing the forwarding delay. If the parameter is configured as the automatic mode, MSTP can automatically detect whether the current Ethernet port is connected to a point-to-point link. Note that: for an aggregation port, only the link type of the primary port of the aggregation port can be configured as point-to-point; if a port operates in the auto-negotiation mode and the negotiated operation mode is the full duplex mode, the link type of the port can be configured as point-to-point. The configuration is valid for the CIST and all MSTIs. When the link type of a port is set to point-to-point or non-point-to-point, the link type of the port is set to point-to-point link or non-point-to-point on all spanning tree instances. If the actual physical link of a port is not a point-to-point link and you forcibly configure the link as a point-to-point link, temporary loops may occur. By default, this parameter is auto.
• Trans Limit(packets/hello-time): Configure the maximum transmitting rate for the port. It is related to the physical state and the network structure of the port, and the user can configure the maximum transmitting rate as required. Note that: the larger the parameter is configured, the more the packets are sent per unit time, consequently occupying more network resources. We recommend that you use the default settings. By default, the maximum transmission rate for all Ethernet ports on the switch is 3 (it is the value of the counter, and no unit is assigned to it).
• Port MSTP Status: To enable a switch to operate more flexibly, you can disable MSTP on specific ports. As MSTP-disabled ports do not participate in spanning tree calculation, this operation saves CPU resources of the switch. By default, MSTP is enabled for all ports after it is enabled for the device globally.
• Root Protection: The root switch and backup switch of the spanning tree shall be within the same region, especially the root switch and backup switch of the CIST. Generally, the root switch and backup switch of the CIST will be placed in the core region of high bandwidth upon network design. Sometimes, due to the error configurations by the maintenance staff or vicious attacks by users, the current valid root switch may receive the configuration messages of higher priority, in which way the current root switch loses its status as the root switch and causes the incorrect change of the network topology structure. Such invalid changes may cause the traffic, which should be transmitted over the high-speed link, to be pulled to the low-speed link, resulting in network congestion. You can avoid this problem by enabling the root guard function. For a port configured with the root guard function, the port role on all instances can only be the designated port. Once this port receives BPDUs with higher priority, that is, it is selected as a non-designated port, it enters the discarding state and does not forward packets any longer (this is equal to disconnecting the links connected to this port). When the priority of the received BPDUs is lower than that of the local BPDUs, the port will automatically migrate from the listening state, via the intermediate state, to the normal forwarding state. The root guard function is disabled by default.
• Mcheck: Force the device to operate in MSTP mode. Ports on an MSTP-enabled switch can operate in STP-compatible mode or MSTP mode. In a switched network, if a port on the device running MSTP connects to a device running STP, this port will automatically migrate to the STP-compatible mode. However, if the device running STP is removed, this will not be able to migrate automatically to the MSTP mode, but will remain working in the STP-compatible mode. In this case, you can set the mCheck parameter to force the port to migrate to the MSTP mode.
• Clear Statistics: Clear the port MSTP monitoring entries. The following part describes the port MSTP monitoring entries in details.
• Default Path Cost: Restore the path cost of each port to the default.