[Spud] States in draft-trammell-plus-statefulness-00

Dave Dolson <ddolson@sandvine.com> Fri, 11 November 2016 10:55 UTC

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From: Dave Dolson <ddolson@sandvine.com>
To: "mirja.kuehlewind@tik.ee.ethz.ch" <mirja.kuehlewind@tik.ee.ethz.ch>, "hildjj@cursive.net" <hildjj@cursive.net>, "ietf@trammell.ch" <ietf@trammell.ch>
Thread-Topic: States in draft-trammell-plus-statefulness-00
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Date: Fri, 11 Nov 2016 10:55:34 +0000
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Subject: [Spud] States in draft-trammell-plus-statefulness-00
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Mirja, Brian, Joe,

I think it is an interesting idea to formalize/standardize the state machine that should be used by flow-stateful network equipment.

But having read about the four states and three timeouts, I feel you are missing a state after biflow that represents a fully proven connection.

I'm thinking of the problem of source-spoofed SYN attack packets that attempt to consume state memory in servers and flow-stateful network devices.
A network device may see client SYN and server SYN-ACK but never the completed 3-way handshake because the client is not real.

Until the 3-way handshake is completed, only short timeouts should be used. This is true for server as well as stateful network devices.

The nice thing about the client's ACK of the server's SYN flag is that it echoes back (in the ACK field) the SYN sequence number, which is unlikely to be guessed by an attacking node that doesn't own the address it used in the SYN packet. The ACK packet also carries the original client sequence# + 1, proving it has a stateful connection.

As an alternative to adding a state, you could enter the bi-flow state only when the TCP 3-way handshake is complete.

Does QUIC carry a network-observable signal indicating receipt of the server packet?