Chapter 7: Spanning Tree Protocol (STP) 119
Section 7-2
The port cost can be set to cost (1 to 65535 short or MISTP mode, 1 to 2000000
long mode) for all VLANs or STP instances. The mst keyword signifies a port
used in MST.
c. Set the port cost per VLAN or per instance:
(interface) spanning-tree vlan vlan-id cost cost
The port cost can be set to cost (1 to 65535 short mode, 1 to 2000000 long
mode) for the VLAN vlan-id or the list of VLANs, vlan-list, or STP instance (0
to 15).
8. (Optional) Tune the port priority.
a. Set the port priority for all VLANs or instances:
(interface) spanning-tree port-priority port-priority
The port priority can be set to priority (2 to 255).
b. Set the port priority per VLAN or per instance:
(interface) spanning-tree vlan vlan-list port-priority priority
The port priority can be set to priority (0 to 255) for the VLAN vlan-id or the
list of VLANs, vlan-list, or STP instance (0 to 15).
9. (Optional) Detect unidirectional connections with UDLD.
a. Enable UDLD on the switch:
(global) udld {enable | aggressive}
By default, UDLD is disabled. It must be enabled before it can be used on specif-
ic ports. The Supervisor IOS enables the keyword aggressive to be used to glob-
ally enable UDLD aggressive mode on all Ethernet fiber-optic interfaces.
b. (Optional) Adjust the UDLD message interval timer:
(global) udld message time interval
The UDLD message interval can be set to interval (7 to 90 seconds; COS default
is 15 seconds, Supervisor IOS is 60 seconds).
c. Enable UDLD on specific ports:
(interface) udld {enable | disable}
After UDLD has been globally enabled on a switch, UDLD is also enabled by
default on all Ethernet fiber-optic ports. UDLD is disabled by default on all
Ethernet twisted-pair media ports.
d. (Optional) Enable UDLD aggressive mode on specific ports:
(interface) udld aggressive
After aggressive mode has been enabled on a port, the port is disabled when a
unidirectional connection is detected. It must be manually reenabled after the
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