ipid-debuggery (was Re: [e2e] ICMP & TCP segments with IP ID = 0?

[Craig Partridge]

In message <5.0.2.1.2.20010516172301.00acd200 at uniwest1>, "Kastenholz, Frank" wr
ites:

>Actually, the Frag-ID field is incredibly useful in debugging..
>
>Of course, that's not "real networks", so we now return to our 
>regularly scheduled pin-heads-dancing-on-angels discussion :-)

I'd maintain it is real networks.  Network protocols get used in ways
their designers never imagined -- and fields turn out to have unexpected
uses.

For instance, the reason that my query about the IP ID popped out was that
we're tracing the path taken by IP datagrams by looking at the first 28 or
so bytes of the packet.  If the IP ID is zero, it turns out that lots of
packets for the same conversation look identifical trace their paths.  And
if the IP ID is zero, you turn out to have lots of identical packets...

The interesting question is what status do such efforts have.  If they
make use of a feature in the protocol that everyone is supposed to
implement, and use that feature for a purpose beyond that which the
protocol architects intended is that (a) wrong; (b) a second-class
usage [e.g., they can't complain if people don't implement the feature]; or
(c) a use of the protocol entitled to equal credence with work done before?

Pondering,

Craig