FTOS Configuration Guide for the C-Series - Force10 Networks

To test the condition of cables on 10/100/1000 BASE-T modules, use the tdr-cable-test command:
Step Command Syntax Command Mode Usage
1 tdr-cable-test gigabitethernet
/
2
show tdr gigabitethernet /
Link Dampening
Interface state changes occur when interfaces are administratively brought up or down or if an interface
state changes. Every time an interface changes state or flaps, routing protocols are notified of the status of
the routes that are affected by the change in state, and these protocols go through momentous task of
re-converging. Flapping therefore puts the status of entire network at risk of transient loops and black
holes.
Link dampening minimizes the risk created by flapping by imposing a penalty for each interface flap and
decaying the penalty exponentially. Once the penalty exceeds certain threshold, the interface is put in an
"error-disabled" state, and for all practical purposes of routing, the interface is deemed to be "down." Once
the interface becomes stable and the penalty decays below a certain threshold, the interface comes up again
and the routing protocols re-converge.
Link dampening:
• reduces processing on the CPUs by reducing excessive interface flapping.
• improves network stability by penalizing misbehaving interfaces and redirecting traffic
• improves convergence times and stability throughout the network by isolating failures so that
disturbances are not propagated.
Important Points to Remember
• Link dampening is not supported on VLAN interfaces
• Link dampening is disabled when the interface is configured for port monitoring
• Link dampening can be applied to Layer 2 and Layer 3 interfaces.
EXEC privilege To test for cable faults on the
GigabitEthernet cable.
• Between two ports, you must not start
the test on both ends of the cable.
• You must enable the interface before
starting the test.
• The port should be enabled to run the
test or the test prints an error
message.
EXEC privilege Displays TDR test results.
• Link dampening can be configured on individual interfaces in a LAG.
276 Interfaces