Administrator Guide

Maintenance Using TDR
The time domain reectometer (TDR) is supported on all Dell Networking switch/routers.
TDR is an assistance tool to resolve link issues that helps detect obvious open or short conditions within any of the four copper pairs. TDR
sends a signal onto the physical cable and examines the reection of the signal that returns. By examining the reection, TDR is able to
indicate whether there is a cable fault (when the cable is broken, becomes unterminated, or if a transceiver is unplugged).
TDR is useful for troubleshooting an interface that is not establishing a link; that is, when the link is apping or not coming up. TDR is not
intended to be used on an interface that is passing trac. When a TDR test is run on a physical cable, it is important to shut down the port
on the far end of the cable. Otherwise, it may lead to incorrect test results.
NOTE: TDR is an intrusive test. Do not run TDR on a link that is up and passing
trac.
To test and display TDR results, use the following commands.
1 To test for cable faults on the TenGigabitEthernet cable.
EXEC Privilege mode
tdr-cable-test tengigabitethernet slot/port
Between two ports, do not start the test on both ends of the cable.
Enable the interface before starting the test.
Enable the port to run the test or the test prints an error message.
2 Displays TDR test results.
EXEC Privilege mode
show tdr tengigabitethernet slot/port
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 a state or aps, routing protocols are notied of the status of the routes that are aected by the change in
state. These protocols go through the 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 apping by imposing a penalty for each interface ap and decaying the penalty exponentially.
After the penalty exceeds a 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.” After 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 apping.
• improves network stability by penalizing misbehaving interfaces and redirecting trac.
• 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 congured for port monitoring.
Interfaces
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