Configuring MSTP per-port parameters

[no] spanning-tree <port-list> admin-edge-port

Enables admin-edge-port on ports connected to end nodes. During spanning tree establishment, ports with admin-edge-port enabled transition immediately to the forwarding state. If a bridge or switch is detected on the segment, the port automatically operates as non-edge, not enabled.

Default: Disabled

If admin-edge-port is disabled on a port and auto-edge-port has not been disabled, the auto-edge-port setting controls the behavior of the port.

The no form of this command disables edge port operation on the specified ports.

[no] spanning-tree <port-list> auto-edge-port

Enables the automatic identification of edge ports for faster convergence. When enabled, the port will look for BPDUs for the first 3 seconds. If there are none, the port will be classified as an edge port and it immediately start forwarding packets. If BPDUs are seen on the port, it will be classified as a non‐edge port and normal STP operation will commence on that port.

If admin-edge-port is enabled for a port, the setting for auto-edge-port is ignored whether set to yes or no.

If admin-edge-port is set to no and auto-edge-port has not been disabled (set to no), then the auto-edge-port setting controls the behavior of the port.

Default: Enabled

The no form of this command disables auto-edge-port operation on the specified ports.

spanning-tree <port-list> hello-time [ global | <1 - 10> ]

When the switch is the CIST root, this parameter specifies the interval (in seconds) between periodic BPDU transmissions by the designated ports. This interval also applies to all ports in all switches downstream from each port in the <port-list>.

A setting of global indicates that the ports in <port-list> on the CIST root are using the value set by the global spanning tree hello-time value.

When a given switch X is not the CIST root, the per-port hello-time for all active ports on switch X is propagated from the CIST root and is the same as the hello-time in use on the CIST root port in the currently active path from switch X to the CIST root. When switch X is not the CIST root, then the upstream CIST root's port hello-time setting overrides the hello-time setting configured on switch X.

Default Per-Port setting: Use Global.

Default Global Hello-Time: 2.

spanning-tree <port-list> mcheck

Forces a port to send RST/MST BPDUs for 3 seconds. This tests whether all STP bridges on the attached LAN have been removed and the port can migrate to native MSTP mode and use RST/MST BPDUs for transmission.

spanning-tree <port-list> path-cost [auto | <1..200000000>]

Assigns an individual port cost that the switch uses to determine which ports are forwarding ports in a given spanning tree. In the default configuration (auto) the switch determines a port's path cost by the port's type:

10 Mbps	2000000
100 Mbps	200000
1 Gbps	20000

Default: Auto

spanning-tree <port-list> point-to-point-mac [ true | false | auto ]

Informs the switch of the type of device to which a specific port connects.

true	(Default) Indicates a point-to-point link to a device such as a switch, bridge, or end-node.
false	Indicates a connection to a half-duplex repeater (which is a shared LAN segment).
auto	Causes the switch to set Force-False on the port if it is not running at full duplex.

spanning-tree <port-list> priority <priority-multiplier>

MSTP uses this parameter to determine the port to use for forwarding. The port with the lowest priority number has the highest priority for use.

The range is 0 to 240 and is configured by specifying a multiplier from 0 - 15. When you specify a priority multiplier of 0 - 15, the actual priority assigned to the switch is:

(priority-multiplier) x 16

If you configure 2 as the priority multiplier on a given port, the actual Priority setting is 32. After specifying the port priority multiplier, the switch displays the actual port priority (and not the multiplier) in the show spanning-tree or show spanning-tree <port-list> displays.

You can view the actual multiplier setting for ports by executing show running and looking for an entry in this format:

spanning-tree<port-list> priority <priority-multiplier>

For example, configuring port A2 with a priority multiplier of 3 results in the following line in the show running output:

spanning-tree A2 priority 3

spanning-tree <port-list> root-guard

When a port is enabled as root-guard, it cannot be selected as the root port even if it receives superior STP BPDUs. The port is assigned an "alternate" port role and enters a blocking state if it receives superior STP BPDUs.

A superior BPDU contains both "better" information on the root bridge and path cost to the root bridge, which would normally replace the current root bridge selection.

The superior BPDUs received on a port enabled as root-guard are ignored. All other BPDUs are accepted and the external devices may belong to the spanning tree as long as they do not claim to be the Root device.

Use this command on MSTP switch ports that are connected to devices located in other administrative network domains to:

• Ensure the stability of the core MSTP network topology so that undesired or damaging influences external to the network do not enter.

• Protect the configuration of the CIST root bridge that serves as the common root for the entire network.

Default: Disabled

spanning-tree <port-list> tcn-guard

When enabled for a port, this causes the port to stop propagating received topology change notifications and topology changes to other ports.

Default: Disabled