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Date: Tue, 12 Apr 2016 23:59:33 +1000 (EST)
From: Ian Smith <smithi@nimnet.asn.au>
To: pete wright <nomadlogic@gmail.com>
cc: freebsd-questions@freebsd.org, sathiyaraj v <sathiyarajmca@gmail.com>
Subject: Re: DUMmYNet configuration
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In freebsd-questions Digest, Vol 619, Issue 2, Message: 5
On Mon, 11 Apr 2016 10:13:53 -0700 pete wright <nomadlogic@gmail.com> wrote:
 > On Mon, Apr 11, 2016 at 9:23 AM, sathiyaraj v <sathiyarajmca@gmail.com> wrote:
 > > Hi team,
 > >
 > > I am new to FreeBSD. I want to understand the DUMMYNET concept. How
 > > firewall rules can be applied using dummynet? Is there any socket necessary
 > > to apply the firewall rules? How the rules work internally? Can you please
 > > help me to understand?
 > 
 > 
 > reading the available documentation is probably the best first step.
 > 
 > http://info.iet.unipi.it/~luigi/dummynet/

Yes, that's the best introduction to the concepts, however configuration 
information is consolidated in ipfw(8) (ie, man ipfw) where dummynet has 
its own chapter and some practical examples.

Probably best to subscribe to the freebsd-ipfw@freebsd.org list, and 
hunt through its archives, for a deeper exploration or more questions.

As for how it works internally, you really have to dive into sources.

cheers, Ian