Software for FreeBSD TCP R&D: SIFTR v1.1.4 and DPD v1.0 released

[Lawrence Stewart]

Hi Byung-Hee,

Byung-Hee HWANG wrote:
> On Wed, 2007-10-10 at 11:42 +1000, Lawrence Stewart wrote:
>   
>> Hi All,
>>
>> Just a quick heads up regarding the availability of a new SIFTR
>> (Statistical Information for TCP Research) version and the debut release
>> of DPD (Deterministic Packet Discard).
>>
>> SIFTR v1.1.4 addresses a couple of issues, one of which is applicable to
>> users of SIFTR in FreeBSD 7-CURRENT. Read the changelog and readme for 
>> more information.
>>
>> DPD is a new FreeBSD kernel module we developed to further aid us in our
>> ongoing TCP research. It allows for the deterministic dropping of TCP
>> packets from within the FreeBSD kernel via a simple sysctl interface.
>> This is particularly useful for anyone that is interested in observing
>> TCP reacting to packet loss events (e.g. congestion control
>> researchers). Being able to drop the same packet(s) across multiple
>> tests allows for simpler comparisons of TCP behaviour. We've found it
>> particularly useful in evaluating and observing the behaviour of
>> different congestion control mechanisms, and hope it may be of use to
>> others out there. Please refer to the DPD readme for more in-depth
>> information.
>>
>> The software and documentation is freely available under a BSD licence from:
>>
>> http://caia.swin.edu.au/urp/newtcp/tools.html
>>
>> We would be very happy to hear from anyone regarding bugs and
>> suggestions as well.
>>     
>
> First of all, I would like to thank you for your good efforts. Its
> almost feature seems like PF(4), however, it's useful to me, maybe.
>   

Thanks!

w.r.t. PF, as far as I'm aware, it does not allow the user to drop 
arbitrary packets identified by number within a TCP flow. Dummynet with 
its uniform packet loss pipe configuration is about the closest thing to 
DPD that I know of. The problem with Dummynet's uniform packet loss is 
that you have no control over which packets get dropped, which makes 
analysing TCP behaviour very difficult indeed. That said, I could simply 
be blissfully unaware that such functionality exists in PF.

> Are you willing to support IPv6 for both SIFTR and DPD?
>   
In the short term, our research does not entail the use of IPv6 and 
there is currently insufficient time available for implementing 
functionality that is not immediately useful to us.

That said, it should be fairly straight-forward work to add IPv6 
support, and I'd be more than happy to give you all the pointers and 
tips required to carry out the modifications if you were so inclined.

Cheers,
Lawrence