AltQ + ng_iface

Daniel O'Connor doconnor at
Fri Jul 29 01:45:51 GMT 2005

On Friday 29 July 2005 11:02, Chuck Swiger wrote:
> 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?  :-)

Hmm, I guess you could make those skip the pipe..

> 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...

The theory is that by prioritising outgoing ACKs you don't cause downstream 
delays when your upstream is full. eg

> [ 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? ]

Maybe, but it doesn't appear to do a particularly good job for a lot of 
situations :)

Daniel O'Connor software and network engineer
for Genesis Software -
"The nice thing about standards is that there
are so many of them to choose from."
  -- Andrew Tanenbaum
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