From: Crist J. Clark (crist.clark@attbi.com)
Date: Wed Jun 11 2003 - 13:52:04 EDT
I am looking for a simple tool that I can use to control how TCP data
is split up among segments. I can't seem to figure out how to coax
Netcat into doing this.
What I am trying to do is mess with some firewall/proxy software by
screwing with (unfounded) assumptions it makes about the contents of
individual packets. For example, I am seeing some Widely Used
Commercial Firewall Software choke when an FTP client sends a packet
containing just,
"USER "
That is, U, S, E, R, and a space. The next segment carries the rest of
the line,
"anonymous\r\n"
Now, since TCP is a stream-oriented protocol, this is actually
perfectly acceptable behavior. The TCP stack of the server will handle
this just fine, and the FTP server software will see the perfectly
Standard-compliant input,
"USER anonymous\r\n"
At the other end.
This is an old and well known problem with firewall/proxies, yet we
see it all of the time. The problem I am having is finding a tool that
lets me easily control the data in each segement of the TCP
stream. I've manually crafted some packets with hping2 to do some
testing, but it is a huge PITA to build the whole SYN/SYN-ACK/ACK
handshake each time. Can anyone recommend a tool or show me how to get
Netcat to do this? Or am I going to have to build something myself or
hack Netcat code?
Since this is a well known issue, I was hoping someone already had
done the work and made it available. Thanks.
-- Crist J. Clark | cjclark@alum.mit.edu | cjclark@jhu.edu http://people.freebsd.org/~cjc/ | cjc@freebsd.org --------------------------------------------------------------------------- ----------------------------------------------------------------------------
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