How to you stop outdiscards from occurring on ethernet ports?

[mctiesman]

I have a number of switches being monitored that are reports many outdiscards on various ports. What is the easiest way to prevent outdiscards from occurring on ethernet ports? 

[Leo Laohoo]

Discards on an ethernet port normally happens when the downstream device constantly keeps sending a "pause" frame to the switch.  The switch then sends the intended packets into a buffer pool.  When this buffer gets full, the switch will then discard the oldest packet.  This is when discard counter increments.  

A few ways to manage discards is QoS and another is check the configuration of the downstream device.  

One of the most common causes of discards is when your switch has a very low buffer or memory pool and it couldn't handle micro-burst of data traffic.  This happens when you have a Catalyst switch and you've got high-speed VM as downstream clients.

[mctiesman]

Leo, 

Taking your statement into account, what is a possible solution I could look at implementing on my side to resolve the outdiscards?

[Leo Laohoo]

There are several methods to determine if QoS (or the lack of) is the cause of your discards.  

My favourite is the quick-and-very-dirty method of setting the port to 10/100 Mbps (interface command:  speed auto 10 100) and see if the discards are still incrementing or not.  

[mctiesman]

Most of the ports experiencing the outdiscards are already configured for auto negotiation. 

[stephendrkw]

This maybe a negotiation problem with your specific hosts...... Currently I have an issue with incrementing discards on a bunch of switch ports running 1gb auto, I have a Gigamon aggregator switch tapping these problem switch ports sending each hosts data to a traffic analyzer tool. I can see over 1s period the max bandwidth is 600mb for most hosts (all 1gb links) but if I dig deeper over 1ms and 10ms microbursts I can see the link almost constantly hitting 1GB, ie.- hitting the max. QOS is really not going to make much difference here with my type of traffic, the solution is to go to a 10Gb solution. Not an easy solution, this costs money! How many packets per/sec per 5 min input and output are you seeing? Mine are approx 10,000-15,000 on average on a WS-X6748-GE-TX card. sh int gi1/10