Subject: draft-ietf-ippm-owdp: arbitrary packets?

From: stanislav shalunov <[email-masked]>
Date: 18 Dec 2000 17:01:15 -0500

There was a suggestion made during physical IPPM WG meeting that the
protocol should be modified in such a way as to allow specification of
arbitrary packet format, along with an indication of where within
these packets the actual timestamp is located.

This would address Type-P issue in a rather general way.  (But not
completely, since one can imagine situations where advance
reservations via a bandwidth broker or RSVP would change the results
of a measurement.)

This suggestion seems appealing, however, there are certain
problematic areas that need to be addressed if we want to implement
it.

* Many OWDP-Test speakers will be Unix or other general purpose
  computers.  These will inevitably have higher losses when listening
  to raw network traffic.  Raw sockets will induce higher loss rate
  than one would have with UDP measurements.

* How would one distinguish between a situation where packets aren't
  supposed to be routed to the receiver and situation of 100% loss?

* Carefully crafted packets could cause disruption to some link-layer
  protocols.  How would an implementer decide what to allow so as not
  to increase risks?

* Suppose an identity of an authenticated user becomes compromised.
  Now the attacker could use that to run TCP sessions to rlogin port
  of machines around servers that trust this user to perform
  measurements (or, less drastically, to send spam from that network).
  Ability to perform measurements is transformed into ability to
  generate arbitrary traffic on behalf of all the senders an
  OWDP-Control server controls.

* How do we specify criteria for listening to traffic?  Standartizing
  tcpdump syntax is hardly an option, but what else do we have?

Thoughts?  Should we just stick with UDP plus possibly a few options
for things like PHB/DSCP, TTL, DF, etc.?

-- 
Stanislav Shalunov <[email-masked]>	Internet Engineer, Internet2

Beware of Programmers who carry screwdrivers.    -- Leonard Brandwein