Capwap Mailing List: Re: Issue 168: DTLS and Retransmissions

[Pasi.Eronen (Pasi.Eronen]

Section 2.4.3 assumes that only the WTP retransmits DTLS
messages if it doesn't get a reply (and AC retransmits
a reply only when it gets a retransmitted request from
the WTP).

That's not the case: both parties retransmit if the handshake
isn't done yet. For example, the AC will also keep retransmitting 
ServerHello (and Certificate/ServerKeyExchange/ServerHelloDone)
if it doesn't receive a reply (Certificate/ClientKeyExchange/etc.)
from the WTP.

Best regards,
Pasi

> -----Original Message-----
> From: ext Pat Calhoun (pacalhou) [mailto:pcalhoun [at] cisco.com] 
> Sent: 01 August, 2008 20:12
> To: Charles Clancy
> Cc: capwap [at] frascone.com; Eronen Pasi (Nokia-NRC/Helsinki)
> Subject: RE: [Capwap] Issue 168: DTLS and Retransmissions
> 
> Got it - waiting for Pasi on 2.4.3.
> 
> PatC 
> 
> -----Original Message-----
> From: Charles Clancy [mailto:clancy [at] ltsnet.net] 
> Sent: Friday, August 01, 2008 2:38 AM
> To: Pat Calhoun (pacalhou)
> Cc: capwap [at] frascone.com; Pasi.Eronen [at] nokia.com
> Subject: Re: [Capwap] Issue 168: DTLS and Retransmissions
> 
> Suggested text changes to address the comments:
> 
> Replace this 2.4.1 text:
> 
>     DTLS, as specified, provides its own retransmit timers with an
>     exponential back-off.  However, DTLS will never terminate the
>     handshake due to non-responsiveness; instead, DTLS will 
> continue to
>     increase its back-off timer period.  Hence, timing out incomplete
>     DTLS handshakes is entirely the responsibility of the 
> CAPWAP module.
> 
> with this text:
> 
>     DTLS, as specified, provides its own retransmit timers with an
>     exponential back-off.  [RFC4347] does not specify how long
>     retransmissions should continue.  Consequently, timing out
> incomplete
>     DTLS handshakes is entirely the responsibility of the 
> CAPWAP module.
> 
> I'm not sure what needs to be addressed in 2.4.3.  Pasi -- can you be
> more specific?
> 
> --
> Dr. Charles Clancy                     www.ltsnet.net/~clancy
> Senior Researcher, Laboratory for Telecommunications Sciences
> 
> 
> Pat Calhoun (pacalhou) wrote:
> > Pasi's comment was:
> > 
> >    Section 2.4.1: "DTLS will never terminate the handshake due to
> >    non-responsiveness; instead, DTLS will continue to 
> >    increase its back-off timer period" While RFC 4347 
> doesn't specify 
> > how
> >    long you should continue retransmitting, the 
> >    intent certainly was not to continue indefinitely.
> >  
> >    Section 2.4.3 text about DTLS retransmissions is slightly
> inaccurate;
> >    DTLS handshake isn't strictly request/response, 
> >    and both parties (not just the DTLS client) retransmit based on 
> > timers
> >    (in some situations).
> > 
> > It is unclear to me as to whether these are simply observations, or 
> > request for change. That said, I would like either Charles 
> or Scott to
> 
> > reply.
> > 
> > PatC
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