Re: Efficient use of Dummynet pipes in IPFW
From: Jeremie Le Hen (jeremie_at_le-hen.org)
Date: 09/20/05
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Date: Tue, 20 Sep 2005 09:15:04 +0200 To: Brett Glass <brett@lariat.org>
Hi Brett, Luigi, all,
> >original
> >
> > ipfw add 1000 dosomething cond1 cond2 cond3 cond4 cond5 ... condN
> >
> >negated:
> >
> > ipfw add 1000 skipto 1001 cond1 cond2 cond3 cond4 cond5 ... condN
> > ipfw add 1000 dosomething
>
> This doesn't work, because you must transform cond1 && cond2 && cond3...
> into multiple rules that implement ~(cond1 || cond2 || cond3...). So,
> you'd need do do the following:
>
> ipfw add 1000 skipto 1001 not cond1
> ipfw add 1000 skipto 1001 not cond2
> ... (N rules total)
> ipfw add 1000 skipto 1001 not condN
> ipfw add 1000 dosomething
> ipfw add 1000 skipto 5000 // Where to resume on success
> ipfw add 1001
I tend to agree with Luigi now. I didn't realize this before, but
let's apply De Morgan's theorem. Each condition is identified as
a small letter "a", "b", "c". "/a" means "not a" and the "." operator
is AND, while the "+" operator is OR.
The above "original" rule is therefore : a.b.c
The above "negated" rule is obviously : /(a.b.c)
With your ruleset may be summed up as : /a+/b+/c
Which is the same as the "negated" rule in regard to De Morgan's theorem.
Do you agree with this ?
Regards,
-- Jeremie Le Hen < jeremie at le-hen dot org >< ttz at chchile dot org > _______________________________________________ freebsd-net@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org"
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