Re: [TLS] Lost last DTLS Flight

[Eric Rescorla <ekr at networkresonance.com>]

At Mon, 27 Oct 2008 12:07:59 +0100,
Robin Seggelmann wrote:
> 
> We're still working on DTLS for SCTP and stumbled over a problem with  
> the last flights specified in RFC 4347. The server receives flight 5  
> (Certificate, ..., ChangeCipherSpec, Finished) from the client,  
> changes its state to FINISHED and sends its ChangeCipherSpec and  
> Finished (Flight 6). What happens if this flight gets lost? The  
> server already is in the FINISHED state and as there also is no  
> acknowledgement, so it won't be retransmitted. Hence, the client  
> keeps waiting for the flight to arrive and the connection is most  
> likely to fail.

You're right, this is a bug in the state machine. Nice catch.

ISTM that the way this actually needs to work is that the server needs
to stay in WAITING until 2MSL has expired, in case it receives a
retransmitted Flight 5, in which case it retransmits Flight 6.

That sound right?

-Ekr
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