1# $OpenBSD: ackpri,v 1.3 2006/10/07 04:48:01 mcbride Exp $ 2 3# Use a simple priority queue to prioritize empty (no payload) TCP ACKs, 4# which dramatically improves throughput on (asymmetric) links when the 5# reverse direction is saturated. The empty ACKs use an insignificant 6# part of the bandwidth, but if they get delayed, downloads suffer 7# badly, so prioritize them. 8 9# Example: 512/128 kbps ADSL. Download is 50 kB/s. When a concurrent 10# upload saturates the uplink, download drops to 7 kB/s. With the 11# priority queue below, download drops only to 48 kB/s. 12 13# Replace lo0 with your real external interface 14 15ext_if="lo0" 16 17# For a 512/128 kbps ADSL with PPPoE link, using "bandwidth 100Kb" 18# is optimal. Some experimentation might be needed to find the best 19# value. If it's set too high, the priority queue is not effective, and 20# if it's set too low, the available bandwidth is not fully used. 21# A good starting point would be real_uplink_bandwidth * 90 / 100. 22 23altq on $ext_if priq bandwidth 100Kb queue { q_pri, q_def } 24queue q_pri priority 7 25queue q_def priority 1 priq(default) 26 27pass out on $ext_if proto tcp from $ext_if to any queue (q_def, q_pri) 28 29pass in on $ext_if proto tcp from any to $ext_if queue (q_def, q_pri) 30 31