Subject: Re: [eap] [Pana] Re: Reliable delivery (AD comment)

From: "Glen Zorn (gwz)" <[email-masked]>
Date: Fri, 9 Mar 2007 19:37:15 -0800

Bernard Aboba <mailto:[email-masked]> allegedly scribbled on
Thursday, March 08, 2007 10:26 PM:

>> My conclusion (based upon the actual text of the relevant RFCs rather
>> than anecdotal evidence regarding "well-behaved" RADIUS
>> implementations)
> 
> RFC 2865 already recommends behavior that prevents out-of-order
> delivery. 

Actually, it doesn't.  As I have pointed out repeatedly , the semantics
of the Identifier in RADIUS & EAP are identical.  

> A proposal to strengthen that to a MUST is on the table.  From what I
> can tell, this resolves the issue for RADIUS. 
> 
>> that "well-behaved" EAP implementations do NOT require duplicate
>> detection in the transport any more than do "well-behaved" RADIUS
>> implementations.
> 
> The difference between RFC 3748 and 2865 is that 3748 does not
> recommend a duplicate cache of substantial duration.  

Hmm.  I don't really consider "a short period of time" to convey any
meaningful sense of duration; in any case, see below.

> That makes a
> difference if a duplicate is intermingled with a new packet.  

I believe that the packet flow which I gave in an earlier message
illustrated that a timer-based algorithm is insufficient for duplicate
detection in both RADIUS and EAP if the identifier is allowed to simply
"change" between exchanges.  In fact, I think that timers are
unnecessary: all that is needed to solve the problem is to specify the
semantics of the Identifier to be those of a sequence number with
roll-over.  
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From: Yoshihiro Ohba <[email-masked]>
Date: Fri, 9 Mar 2007 23:44:50 -0500

> semantics of the Identifier to be those of a sequence number with

I agree, and that is what PANA is doing with sequence number.

Yoshihiro Ohba

---

From: "Glen Zorn (gwz)" <[email-masked]>
Date: Fri, 9 Mar 2007 20:57:03 -0800

Yoshihiro Ohba <mailto:[email-masked]> allegedly scribbled on
Friday, March 09, 2007 8:45 PM:

>> illustrated that a timer-based algorithm is insufficient for
>> duplicate detection in both RADIUS and EAP if the identifier is
>> allowed to simply "change" between exchanges.  In fact, I think that
>> timers are unnecessary: all that is needed to solve the problem is
>> to specify the semantics of the Identifier to be those of a sequence
>> number with roll-over. 
>> 
> 

That's fine, but personally I think that it's just good protocol design
to reduce the coupling between layers to the bare minimum required.  RFC
3748 has to its credit the fact that it made explicit the dependency of
EAP upon the delivery characteristics of PPP that were implicit in RFC
2284; unfortunately, it leaves that dependency in place even though a
fix is easy enough.