Reference Guide

To test and display TDR results, use the following commands.
1. To test for cable faults on the GigabitEthernet cable.
EXEC Privilege mode
tdr-cable-test gigabitethernet <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 gigabitethernet <slot>/<port>
Splitting QSFP Ports to SFP+ Ports
Splitting QSFP ports to SFP+ ports is supported on the S4820T platform.
The S4820T platform supports splitting a single 40G QSFP port into four 10G SFP+ ports using one of the supported
breakout cables (for a list of supported cables, refer to the Installation Guide or the Release Notes ).
To split a single 40G port into four 10G ports, use the following command.
• Split a single 40G port into 4-10G ports.
CONFIGURATION mode
stack-unit stack-unit port number portmode quad
– stack-unit: enter the stack member unit identifier of the stack member to reset. The range is from 0 to
11.
– number: enter the port number of the 40G port to be split. The range is from 0 to 47 for 10G ports and 48, 52,
56 and 60 for 40G ports.
Important Points to Remember
• Splitting a 40G port into four 10G ports is supported on standalone and stacked units.
• You cannot use split ports as stack-link to stack a S4820T system.
• The unit number with the split ports must be the default (stack-unit 0).
To verify port splitting, use the show system brief command. If the unit ID is different than 0, it must be
renumbered to 0 before ports are split by using the
stackunit id renumber 0 command in EXEC mode.
• The quad port must be in a default configuration before you can split it into 4x10G ports. The 40G port is lost in
the configuration when the port is split; be sure that the port is also removed from other L2/L3 feature
configurations.
• The system must be reloaded after issuing the CLI for the change to take effect.
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 flaps, routing protocols are notified of the status of the routes that are
affected 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 flapping by imposing a penalty for each interface flap and decaying the
penalty exponentially. After the penalty exceeds a certain threshold, the interface is put in an Error-Disabled state and
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