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

From: "Daniel Warren" <[email-masked]>
Date: Thu, 13 Jun 2002 16:21:01 +0100

Daniel Warren writes:
> > > I don't agree with this interpretation - the spec allows (and even
> > > encourages) use of vendor-specific AVPs instead of vendor-specific
> > > commands and applications. VSAs can be mandatory.
> > 
> > If a VSA is mandatory, then every vendor's equipment has to be able to
> > receive it and understand it's meaning.
> 
> Not true.  Don't confuse the 'M bit' with a "MUST implement"
> requirement.  The 'M bit' only means, "if you don't understand the
> VSA, you must fail the command."
> 
> > If the NAS does not understand the VSA, again it has to fail the
> > command, because if the VSA was not essential to the operation, it
> > would not be mandatory.  But to maintain interop, the NAS has to be
> > able to complete the command without the VSA.  Hence there is a
> > contradiction in the logic.  Mandatory implies understanding, but
> > interop requires it to be ignored.  You can't have both.
> 
> I think Bernard's point was that failing a command is a perfectly
> valid way to interop, especially for security-related commands.  If
> the sender gets a failure indication, it can try something else, like
> re-sending the command without the offending VSA, or giving up.
> 

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.

---

From: Pete McCann <[email-masked]>
Date: Thu, 13 Jun 2002 10:35:06 -0500

> 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