[Snort-users] T/TCP resources -- answer for Andy Wood

Richard Bejtlich richard_bejtlich at ...131...
Thu May 1 16:46:03 EDT 2003


Lots of people have mentioned how to disable T/TCP in
Snort, but no one mentioned what it is -- so far as my
search of the list archives goes.  :)

T/TCP recognizes that many sessions are
request-response, like HTTP, so T/TCP tries to
minimize overhead.  For example, the client sends a
SYN/request/FIN in one packet.  The server sends its
SYN/ACK/response/FIN, and the session concludes with
the client ACKing the server's FIN.  

For those who want more than my simplistic rendition
of the protocol, see RFC 1379

Other resources include:

T/TCP home page:


1998 Phrack Article by Route:


As for why you're seeing so much traffic which matches
Snort's T/TCP checking code, I'd have to see some raw
captures to analyzing what's happening.


Richard Bejtlich
richard at taosecurity dot com

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