Output buffers swapped out counter

[anup.anand]

Hi,

On a HSSI interface, we are seeing that the OUTPUT BUFFER SWAPPED OUT counter is incrementing at a very high rate (it was 48233551 when we checked last time). As per documents, this value means "Number of output buffer allocation failures". From the show buffers output, the only misses are for small buffers - 161 misses. So it doesn't seem like the router is running out of buffers. This is on a Cisco 7500. Please advise. Thanks in advance.

Here is a part of the show interface output

5 minute output rate 1990000 bits/sec, 519 packets/sec

597391597 packets input, 3425437235 bytes, 0 no buffer

Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

0 parity

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

576136927 packets output, 2216688796 bytes, 0 underruns

0 output errors, 0 applique, 0 interface resets

0 output buffer failures, 48233551 output buffers swapped out

[deilert]

This is not an issue , output buffers swapped out occur when the TX queue on the interface is full , so instead of dropping the packet the router stores the packet in a system buffer instead of dropping it , When space on the TX queue becomes avail it is copied onto the TX ring then transmitted. When this happens the counters increments.

[anup.anand]

Thanks for your response. In that case, increasing the output queue size might be of some help, right. We have increased the output queue length using the hold-queue command. Still monitoring the interface. I will keep posted the results of the change.