Re: [arch-d] deprecating Postel's principle- considered harmful

[Henning Schulzrinne <[e-mail]>]

It's kind of the inverse robustness problem - lots of perfectly-well
documented protocol features are not usable in practice since they break
"lazy", but important, implementations. The SIP crowd will remember the
endless discussions about MIME multipart.

In those cases, it would probably be wise to simply declare that a
well-intentioned feature is no longer recommended for new implementations
and possibly look for alternative options. (We seem to get into the
circular arguments of "We need X", "use standard mechanism M to do X", "but
none of the major implementations do M and are unlikely to in the
foreseeable future", "but we cannot have two ways to do X and M is actually
a better idea"; wait two years; repeat. Alternative: people develop a
kludge that kind of works.)

The old, rarely-exercised, promotion-to-Draft-Standard step was supposed to
catch this, but that process protocol path obviously was also rarely
exercised.

Henning


>
> And then for a counter example, also related to IPv6. The IPv6 specs
> allows implementations to insert a variety of intermediate headers
> between the IPv6 header and the transport packet, but many router
> implementations just don't like that and slow down or drop packets if
> such intermediate routers are present. A case where the spec is arguably
> too permissive, or the implementations too strict.
>
> -- Christian Huitema
>
>