1# $FreeBSD$ 2# $OpenBSD: ackpri,v 1.3 2006/10/07 04:48:01 mcbride Exp $ 3 4# Use a simple priority queue to prioritize empty (no payload) TCP ACKs, 5# which dramatically improves throughput on (asymmetric) links when the 6# reverse direction is saturated. The empty ACKs use an insignificant 7# part of the bandwidth, but if they get delayed, downloads suffer 8# badly, so prioritize them. 9 10# Example: 512/128 kbps ADSL. Download is 50 kB/s. When a concurrent 11# upload saturates the uplink, download drops to 7 kB/s. With the 12# priority queue below, download drops only to 48 kB/s. 13 14# Replace lo0 with your real external interface 15 16ext_if="lo0" 17 18# For a 512/128 kbps ADSL with PPPoE link, using "bandwidth 100Kb" 19# is optimal. Some experimentation might be needed to find the best 20# value. If it's set too high, the priority queue is not effective, and 21# if it's set too low, the available bandwidth is not fully used. 22# A good starting point would be real_uplink_bandwidth * 90 / 100. 23 24altq on $ext_if priq bandwidth 100Kb queue { q_pri, q_def } 25queue q_pri priority 7 26queue q_def priority 1 priq(default) 27 28pass out on $ext_if proto tcp from $ext_if to any queue (q_def, q_pri) 29 30pass in on $ext_if proto tcp from any to $ext_if queue (q_def, q_pri) 31 32