TCP Daytona in userland

[Julian Elischer]

Andrea Campi wrote:

>Hi all,
>
>I have started working on a "TCP Daytona" implementation [1]. I'm
>quite familiar with TCP/IP in theory, and sort of familiar with the
>BSD implementation ideas, but looking into tcp_input and tcp_output is
>always a mistic experience ;-) I tried to understand how I could
>generate multiple (either duplicate or better partial ACKs), but I
>guess tcp_output is really not meant to do such a thing. Does anyone
>have an idea of how hard would it be to generate more than one ACK for
>an input packet, and could you give me some suggestion?
>
>So to get my feet wet, I've decided to start from a simple userland
>implementation using BPF. Currently I'm using a test program that does
>an HTTP transfer and, from a parallel thread, I monitor the
>conversation and send additional ACKs for each genuine ACK I see. This
>doesn't seem to have any (positive or negative) effect if I send 1 or
>2 duplicate ACKs, but slows the connection down if I send 3 or more
>additional ACKs. I didn't have much time to investigate this yet.
>
>Sadly, this wouldn't work if I wanted to send partial ACKs instead.
>What would be nice is to be able to stop the genuine ACK from being
>sent and inject partial ACKs instead. Do we have any mechanism that
>would allow me to do this? Maybe I should be using divert(4) instead?
>  
>

use netgraph with the ng_ether and the ng_etf filter to separate out IP 
packets and send them to you?

if you use divert then re-injecting packets will put them out through 
ip_output
which is probably not what you want.


>Lastly, if anybody already worked on this: do you have any additional
>suggestion? In particular regarding the testing methodology: since a
>few years have passed, I'm not quite sure whether different OSs have
>implemented any countermeasure. I'm mainly testing against a FreeBSD
>box I control, and I don't think we have any defence against this yet.
>
>Bye,
>	Andrea
>
>1. as per the Savage et al. paper:
>http://www-cse.ucsd.edu/~savage/papers/CCR99.pdf
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>  
>