API Guide

Dynamic path cost calculation
Path cost of an interface (physical or port-channel) is calculated based on the speed of the port or port-channel. When the
speed of the port or port-channel changes, the past cost recalculation is triggered based on the user defined configuration.
You can enable/disable dynamic recalculation of path cost using the spanning-tree path-cost command.
This cmd allows the protocol to do dynamic cost calculation whenever the channel-members are added or deleted. By default,
this dynamic path cost calculation is enabled.
When dynamic path cost is disabled , protocol calculate the path cost when the port channel is coming up for the first time after
creation or whenever dynamic path cost calculation is enabled and then disabled by management or when the user adds/
removes member port to/from the port channel.
This feature allows the user to disable path cost re-calculation on link flap events. If disabled, the path cost of the lag is
calculated based on the below formula LAG speed = speed of a single member * number of configured member ports
(irrespective of its oper status).
Path cost changes only for the user event [addition/removal of channel-member]. Path cost is calculated based on the number
of configured ports.
Dynamic path cost disable functionality is supported for VLT port channel.
Debug facilities
Use the debug spanning-tree bpdu command to monitor and verify that the MST configuration is communicating as
configured. To ensure all necessary parameters match — region name, region version, and VLAN to instance mapping, examine
your individual devices. Use the show spanning-tree mst command to view the MST configuration, or use the show
running-configuration command to view the overall MST configuration.
MST flags for
communication
received from
the same region
The MST routers are located in the same region. If the debug logs indicate that packets are coming from
a Different Region, one of the key parameters does not match.
MST region name
and revision
The configured name and revisions must be identical among all devices. If the region name is blank, a
name was configured on one device and was not configured or was configured differently on another —
spelling and capitalization count.
MST instances Verify the VLAN-to-MST instance mapping using the show commands. If you see extra MST instances in
the Sending or Received logs, an additional MST instance was configured on one router but not the
others.
● View BPDUs in EXEC mode.
debug spanning-tree bpdu
● View MST-triggered topology change messages in EXEC mode.
debug spanning-tree events
View MST configuration
OS10# show spanning-tree mst configuration
Region Name: force10
Revision: 100
MSTI VID
0 1,31-4093
1 2-10
2 11-20
3 21-30
EdgePort
EdgePort allows the interface to forward traffic approximately 30 seconds sooner as it skips the Blocking and Learning states.
Layer 2
471