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Date:      Mon, 15 Nov 1999 15:12:12 UTC-0800
From:      Mark McCutcheon <>
Subject:   Re: TOS support for FreeBSD
Message-ID:  <"16582*"@MHS>

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On Sun, 14 Nov 1999 12:56:49 UTC-0500 Crist J. Clark
  <> wrote:

> The trouble is, where would you add this TOS rewrite?... Maybe a
> tool that IPFW diverts the packets of interest to?

You're right, this functionality does NOT belong in ipfw. 
TOS-mediated preferential service for flows is a diffserv per-hop
behaviour, and should be implemented as a queuing discipline.  By
good fortune, it already has been; this is one of the modes of CBQ
(class-based queuing) as it appears in v2.0 of Kenjiro Cho's ALTQ

v2.0 runs mostly on ethernet and ATM NICs, but there is a new PPP
link version (see website).

Since wildcards may be used in the CBQ configuration filters, a
flow may consist of just a protocol type and TOS mask.  ALTQ is
intended for UNIX-based router forwarding research, so it may seem
a bit heavy-weight for a single user wanting to give minimum delay
to telnet.  On the other hand, it's not all that hard to set up,
seems to work as advertised, and puts the queue control where it

Caveat:  I haven't used ALTQ in the common home-use scenario of a
FreeBSD PC running ipfw and natd, so can't say whether there could
be any adverse interaction between ALTQ and natd.

Mark McCutcheon | UBC High-Speed Networking | <>

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