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The %SYS-3-PORT_OUT_DISCARD: intermittent port error messages are received in Catalyst 6500 Series Switches that run CatOS software


Core issue

These messages mean that there are a number of outbound packets chosen to be discarded even though no errors are detected.

If you have a large number of deferred frames, or Out-Discard, which is also referred to as Out-Lost on some platforms, it means that the output buffers of the switch have filled and the switch had to drop these packets. This can be a sign that this segment runs at an inferior speed and/or duplex, or too much traffic goes through this port.

When you have traffic that comes from several ports towards another port of the same speed, or traffic that comes from a GigabitEthernet into a FastEthernet, a short intense burst of traffic can oversubscribe the egress buffers, which leads to outdiscards. This can be a normal behavior under these situations.

For CatOS, use the show mac command for the module and port or the entire module to look at Out-Discards.

In some scenarios, these messages are observed on a destination port of a Switched Port Analyzer (SPAN) session, which can be a normal behavior.


In order to run a complete diagnostic test on the module and check for any problems, complete these steps:

  1. Issue the set test diaglevel complete command in the global configuration mode in order to set the diagnostics level to complete.

  2. Issue the reset [Module Num] command in order to soft-reset the module. After the module works again, capture the output of the show module command and the show test command in order to display the errors reported from the diagnostic tests.

  3. Physically pull out and reseat the module firmly in the chassis in order to hard-reset the module. After the module works again, capture the output of the show module command and the show test command.

For further assistance and support, use the TAC Service Request Tool in order to contact Cisco Technical Support.

Refer to the Deferred Frames (Out-Lost or Out-Discard) section of Troubleshooting Switch Port and Interface Problems for more information.

Problem Type

Port message received

Syslog error message received

Problem frequency


Catalyst switch

Catalyst 6000 series switches

Catalyst 6500 series switches

Switch software

CatOS system software

Error message


Show interface

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