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IfOutDiscards on 6509 Interface

The following is Cisco's explanation, but what type of discard errors would cause this field to increase or I don't need to be concerned?? (BAd NIC Card, Cable Etc.)

The number of outbound packets which were chosen to

be discarded even though no errors had been detected

to prevent their being transmitted. One possible

reason for discarding such a packet could be to free

up buffer space.

2 REPLIES
Cisco Employee

Re: IfOutDiscards on 6509 Interface

From http://www.cisco.com/warp/public/473/53.shtml#frames

Deferred Frames (Out-Lost or Out-Discard)

If you have a large number of deferred frames, or out-lost frames, it means that the switch's output

buffers have filled up and the switch had to drop these packets. This could be a sign that this

segment is running at an inferior speed and/or duplex, or that there is too much traffic going

through this port.

Inferior Speed/Duplex for the Amount of Traffic

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. Consider moving the device hanging off this port to faster media

(for example, if the port is 10 Mbps, move this device to a 100 Mbps or Gigabit port), or changing

the topology to route frames differently.

Segment Too Busy

If the segment is shared, other devices on this segment may be transmitting so much that the

switch has no opportunity to transmit. Consider removing some devices off of this segment to another

segment to give the switch more opportunity to transmit.

Applications Being Used

At times the traffic transmission characteristics of the applications being used can lead to this

occurring. NFS file transfers coming from a Gigabit attached server using user datagram protocol

(UDP) and a 32 K window size is one example of an application setting that could bring out this type

of problem. If you have checked or tried the other suggestions (checked speed/duplex, no physical

errors on the link, all the traffic is normal valid traffic, and so on), then reducing the unit size

being sent by the application may help alleviate this problem.

Note: Out-lost is also noted as Out-discard in some platforms.

You can also reference

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/sw5_1/comdref/sh_d_i.htm#xtocid51470 for

more info on "show counters" output.

Cisco Employee

Re: IfOutDiscards on 6509 Interface

It's unlikely to be due to a bad nic or cable. The counter reports drops that are not the result of an error. What is the traffic like for this port? Do the discards coincide with bursts of traffic? As your note stated this is likely due to congestion (which can appear in bursts).

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