Output_discard Errors

Unanswered Question
Aug 22nd, 2007

What are these output discard errors and how to fix them? I have started to see tons of them in 6509s ever since I upgrade to 8.5.2?

007 Aug 22 02:45:31 %SYS-3-PORT_OUT_DISCARD:Port 2/15 detected 52051 output discard error(s) in last 30 minutes

2007 Aug 22 02:45:31 %SYS-3-PORT_OUT_DISCARD:Port 2/16 detected 51512 output discard error(s) in last 30 minutes

2007 Aug 22 03:15:33 %SYS-3-PORT_OUT_DISCARD:Port 1/5 detected 161034 output discard error(s) in last 30 minutes

2007 Aug 22 03:15:34 %SYS-3-PORT_OUT_DISCARD:Port 1/6 detected 172356 output discard error(s) in last 30 minutes

2007 Aug 22 03:15:34 %SYS-3-PORT_OUT_DISCARD:Port 1/8 detected 161025 output discard error(s) in last 30 minutes

2007 Aug 22 03:15:34 %SYS-3-PORT_OUT_DISCARD:Port 1/10 detected 161210 output discard error(s) in last 30 minutes

2007 Aug 22 03:15:34 %SYS-3-PORT_OUT_DISCARD:Port 1/12 detected 161851 output discard error(s) in last 30 minutes

2007 Aug 22 03:15:34 %SYS-3-PORT_OUT_DISCARD:Port 1/14 detected 161060 output discard error(s) in last 30 minutes

2007 Aug 22 03:15:34 %SYS-3-PORT_OUT_DISCARD:Port 1/16 detected 161348 output discard error(s) in last 30 minute

Thanks.

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Jagdeep Gambhir Wed, 08/22/2007 - 15:49

Nawas,

This error message indicates that a number of outbound packets are being discarded even though they are valid. One reason for this could be that you are sending more traffic than the port can handle.

You won't see any errors on the port itself, instead you could monitor inbound and outbound traffic on the port using the commands

'Show Mac mod/port'(for CatOS).

Your network may be sending too many packets through this port for the port to handle at its current speed/duplex setting. This could happen where you have multiple high-speed ports flowing to a single (usually slower) port. When you have traffic coming from several ports towards another port of the same speed, or traffic coming from a GigabitEthernet into a FastEthernet, a short intense burst of traffic may oversubscribe the egress buffers, which leads to outdiscards.

I would recommend to use the commands below to monitor the ports:

Console> (enable) clear counters all

Then have a few minutes traffic, then capture the following:

Console> (enable) show mac mod/port

- Basic command which helps us to relate the in/out discards with the total traffic in

both packet count and byte count (we can then infer packet size, etc.)

Console> (enable) show mac util mod/port

- Provides an average load indication of the port (on a 5 minute interval by default)

Console> (enable) show counter mod/port

- Extended command which keeps track of number of packets switched per packet size, as well as some of the drop reasons.

I don't think there is issue with switch performance, kind of cosmetic issue.

Regards,

~Jg

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