Configuring MSTP per-port parameters
In an MSTP topology, per-port parameters are
set in the global configuration context. In most cases, Hewlett Packard
Enterprise recommends that you use the default settings for these
parameters and apply changes on a per-port basis only where a non-default
setting is clearly indicated by the circumstances of individual links.
Some port parameters (such as admin-edge-port
)
affect all MSTI instances that consist of VLANs configured on the
port. Other port parameters (such as path-cost
)
affect only the specified MST.
Enabling immediate transition to forwarding on end nodes
Syntax:
[no]
spanning-tree
<port-list>
admin-edge-portEnables
admin-edge-port
on ports connected to end nodes. During spanning tree establishment, ports withadmin-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 andauto-edge-port
has not been disabled, theauto-edge-port
setting controls the behavior of the port.The
no
form of this command disables edge port operation on the specified ports.
Identifying edge ports automatically
Syntax:
[no]
spanning-tree
<port-list>
auto-edge-portEnables 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 forauto-edge-port
is ignored whether set to yes or no.If
admin-edge-port
is set to no andauto-edge-port
has not been disabled (set to no), then theauto-edge-port
setting controls the behavior of the port.Default: Enabled
The
no
form of this command disablesauto-edge-port
operation on the specified ports.
Specifying the interval between BPDU transmissions
Syntax:
spanning-tree
[<port-list>
hello-timeglobal
|]
<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 treehello-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 thehello-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 porthello-time
setting overrides thehello-time
setting configured on switch X.Default Per-Port setting: Use Global.
Default Global Hello-Time: 2.
Determining which ports are forwarding ports by assigning port cost
Syntax:
Informing the switch of the device type to which a port connects
Syntax:
Determining which port to use for forwarding
Syntax:
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 theshow spanning-tree
orshow spanning-tree
displays.<port-list>
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 theshow running
output:
spanning-tree A2 priority 3
Denying a port the role of root port
Syntax:
spanning-tree
<port-list>
root-guardWhen 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