IP protocol performance tuning recommendations

This section provides recommendation for optimizing IP protocol performance.

At the IP layer, the only tunable parameter is ipqmaxlen, which controls the length of the IP input queue. In general, interfaces do not do queuing. Packets can arrive very quickly and overrun the IP input queue. You can use the netstat -s or netstat -p ip command to view an overflow counter (ipintrq overflows).

# no -o ipqmaxlen=100

This example allows 100 packets to be queued up. The exact value to use is determined by the maximum burst rate received. If this cannot be determined, using the number of overflows can help determine what the increase should be. No additional memory is used by increasing the queue length. However, an increase may result in more time spent in the off-level interrupt handler, because IP will have more packets to process on its input queue. This could adversely affect processes needing CPU time. The trade-off is reduced packet-dropping versus CPU availability for other processing. It is best to increase ipqmaxlen by moderate increments if the trade-off is a concern in your environment.