Subject: RE: [AAA-WG]: Mandatory Vendor-specific AVP's

From: "Daniel Warren" <[email-masked]>
Date: Thu, 13 Jun 2002 16:57:31 +0100

> > OK, I can see that point, but mandatory in my mind is with regard to the
> > inclusion of the AVP in the command.  If an AVP (be it standardised or
VSA)
> > is mandatory it has to be in the command as it is essential to the
> > successful completion of the command.  If you are giving the sender the
> > option of trying again without the VSA, then it is not mandatory, it is
> > optional, because you have the option to leave it out without affecting
the
> > completion of the command.
> 
> Ah, but the retry need not be exactly the original minus the VSA.  It
> might change other aspects of the command, so that, for example, if
> the NAS didn't implement the super-terrific-proprietary-security
> mechanism, it could fall back to the
not-quite-as-terrific-but-standardized 
> security mechanism (not such a good example, as it might be open to
> bidding-down attacks, but you get the idea).  Or, the sender could try
> a completely different command instead.
> 
> I agree that all VSAs in standard commands must be "optional" in the
> sense that the ABNF would use [], not {}.  But this doesn't have
> anything to do with the setting of the M-bit.
> 
> -Pete

Ah ha!  So we have got to the bottom of this and (as I was a beginning to
suspect) it comes down to my personal confusion.  I certainly can see the
point you make with regard to the retry.  The bit (no pun intended) that has
really had me baffled is how you could have the M-bit set but not include
the AVP all the time.  The 'real' optionality of an AVP in a command is
indicated in the ABNF, so you could set an M-bit for an AVP contained in
[]'s.

In summary, setting the Mandatory bit doesn't mandate inclusion of the AVP,
rather it mandates that the receiver must understand the AVP, or else fail
the command.  To make sure I am 100% clear, when Bernard and others refer to
a Mandatory VSA, we are talking about setting the M bit, and not mandatory
inclusion.  If that is the case I think I have got my understanding
straight.  I'm not saying it's logical, but I think I get it.

Dan