RFC 3668:Intellectual Property Rights in IETF Tech...
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8. Evaluating alternative technologies in IETF working groups

   In general, IETF working groups prefer technologies with no known IPR
   claims or, for technologies with claims against them, an offer of
   royalty-free licensing.  But IETF working groups have the discretion
   to adopt technology with a commitment of fair and non-discriminatory
   terms, or even with no licensing commitment, if they feel that this
   technology is superior enough to alternatives with fewer IPR claims
   or free licensing to outweigh the potential cost of the licenses.

   Over the last few years the IETF has adopted stricter requirements
   for some security technologies.  It has become common to have a
   mandatory-to-implement security technology in IETF technology
   specifications.  This is to ensure that there will be at least one
   common security technology present in all implementations of such a
   specification that can be used in all cases.  This does not limit the
   specification from including other security technologies, the use of
   which could be negotiated between implementations.  An IETF consensus
   has developed that no mandatory-to-implement security technology can
   be specified in an IETF specification unless it has no known IPR
   claims against it or a royalty-free license is available to
   implementers of the specification unless there is a very good reason
   to do so.  This limitation does not extend to other security
   technologies in the same specification if they are not listed as
   mandatory-to-implement.

   It should also be noted that the absence of IPR disclosures is not
   the same thing as the knowledge that there will be no IPR claims in
   the future.  People or organizations not currently involved in the
   IETF or people or organizations that discover IPR they feel to be
   relevant in their patent portfolios can make IPR disclosures at any
   time.

   It should also be noted that the validity and enforceability of any
   IPR may be challenged for legitimate reasons, and the mere existence
   of an IPR disclosure should not automatically be taken to mean that
   the disclosed IPR is valid or enforceable.  Although the IETF can
   make no actual determination of validity, enforceability or
   applicability of any particular IPR claim, it is reasonable that a
   working group will take into account on their own opinions of the
   validity, enforceability or applicability of Intellectual Property
   Rights in their evaluation of alternative technologies.

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