Re: [fw-wiz] Source of T/TCP traffic

From: Knut Bjornstad (
Date: 09/09/03

  • Next message: Mikael Olsson: "Re: [fw-wiz] Source of T/TCP traffic"
    To: Volker Tanger <>,
    Date: Tue, 9 Sep 2003 19:36:43 +0200

    On Tue, Sep 09, 2003 at 02:22:58PM +0200, Volker Tanger wrote:
    > Greetings!
    > On Tue, 9 Sep 2003 Knut Bjornstad <> wrote:
    > > Our IDS are seeing a lot of peculiar T/TCP traffic - the alerts on
    > > this is no problem in itself - I can easily disable them. But when I
    > > try to analyze the traffic, it seems like ordinary web traffic from
    > > various MS IE sources.
    > Do you see T/TCP, TAO or the braindead MS-IE/IIS speedup hack? Usually
    > newer IE try to send the HTTP request already in the SYN packet (or was
    > it first sending an ACK packet with the request?) ignoring the usual
    > need for a SYN - SYN/ACK - ACK handshake for a proper TCP connection.
    > While the IIS answers directly other servers respond with a RST, upon
    > which the IIS starts anew with the standard 3-way handshake. This way
    > a MS-IE/MS-IIS pair has a small speed advantage over standard clients
    > or servers. It's called improving industry standards, I fear.
    > If this is the traffic you see, you can safely ignore it (as MS-IE
    > does).
    What I see is not - I repeat not - the cheating MS-IE/IIS speedup hack.
    (For this see: )
    I see SYN packets with proper CC.NEW TCP options. They come from a
    handful of Scandinavian providers serving solid customers. We dont get
    anything more of the T/TCP TAO because we have no T/TCP ourselves, and
    then what is sending this falls back to ordinary TCP in accordance with
    the protocol. Further there is quite clear indications of NAT source
    adresses - the browser field in our weblogs vary with the same source among
    other things. I am pretty sure this is one or several different devices
    inserting T/TCP by rewriting the header - but I lack proof.

    So what is this?

    --Knut Bjornstad -- ErgoIntegration AS ---Oslo, Norway------- -- t:47 23 14 53 36 -- mob: 901 15 917 --
    firewall-wizards mailing list

  • Next message: Mikael Olsson: "Re: [fw-wiz] Source of T/TCP traffic"