AltQ + ng_iface

Chuck Swiger cswiger at
Fri Jul 29 01:32:25 GMT 2005

Daniel O'Connor wrote:
> On Friday 29 July 2005 10:10, Julian Elischer wrote:
[ ... ]
>>ipfw and dummynet work on ng_iface I believe.
> Well yeah, but dummynet is a little inflexible and can't prioritise ACKs (for 
> example)

Either the "established" or the "tcpflags !syn,ack" keywords in a rule adding 
matching packets to a high-priority queue ought to do it...?  Or perhaps you 
meant something more specific than just "TCP packets with TH_ACK" set?  :-)

Anyway, I'm not convinced that trying to classify packets within an established 
TCP connection in order to place them on different queues is a really good 
idea, since you're quite likely to reorder the packets by doing so.  I'd expect 
both latency and bandwidth of a TCP connection to suffer very noticably if more 
than 10% or so of the packets arrive out of order...

[ Hmm.  I suppose that one could make an exception to the above generalization 
if URG was set, but the TCP stack already makes an effort to prioritize and 
deliver out-of-band urgent stuff as quickly as possible, anyway, right? ]


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