On Jun 10, 2025, at 4:22 PM, Carlos Pignataro <cpign...@gmail.com> wrote:

> 3. I recommend adding an Experimental range 
> https://datatracker.ietf.org/doc/html/rfc8126#section-4.2

To quote that section:

   Experimental Use is similar to Private Use, but with the purpose
   being to facilitate experimentation.  See [RFC3692] for details.
   IANA does not record assignments from registries or ranges with this
   policy (and therefore there is no need for IANA to review them) and
   assignments are not generally useful for broad interoperability.
   Unless the registry explicitly allows it, it is not appropriate for
   documents to select explicit values from registries or ranges with
   this policy.  Specific experiments will select a value to use during
   the experiment.

   When code points are set aside for Experimental Use, it's important
   to make clear any expected restrictions on experimental scope.  For
   example, say whether it's acceptable to run experiments using those
   code points over the open Internet or whether such experiments should
   be confined to more closed environments.  See [RFC6994] for an
   example of such considerations.

The abstract of RFC 3692 says:

   When experimenting with or extending protocols, it is often necessary
   to use some sort of protocol number or constant in order to actually
   test or experiment with the new function, even when testing in a
   closed environment.  For example, to test a new DHCP option, one
   needs an option number to identify the new function.  This document
   recommends that when writing IANA Considerations sections, authors
   should consider assigning a small range of numbers for
   experimentation purposes that implementers can use when testing
   protocol extensions or other new features.  This document reserves
   some ranges of numbers for experimentation purposes in specific
   protocols where the need to support experimentation has been
   identified.

I'm not sure what an experiment with a link-layer header type would be. The two 
possibilities I can see are:

1) you're experimenting with a new link layer, and want a LINKTYPE_ to use when 
recording traffic over that link layer;

2) you're experimenting with an existing link layer that lacks a LINKTYPE_ 
value, and are testing various options to see how well they work in 
libpcap/tcpdump/Wireshark/etc..

RFC 3692 says

   Numbers in the experimentation range are similar to those called
   "Private Use" in RFC 2434 [IANA-CONSIDERATIONS].  They are not
   intended to be used in general deployments or be enabled by default
   in products or other general releases.  In those cases where a
   product or release makes use of an experimental number, the end user
   must be required to explicitly enable the experimental feature and
   likewise have the ability to chose and assign which number from the
   experimental range will be used for a specific purpose (i.e., so the
   end user can ensure that use of a particular number doesn't conflict
   with other on-going uses).  Shipping a product with a specific value
   pre-enabled would be inappropriate and can lead to interoperability
   problems when the chosen value collides with a different usage, as it
   someday surely will.

RFC 2434's description of "Private Use" is

    Private Use - For private or local use only, with the type and
           purpose defined by the local site. No attempt is made to
           prevent multiple sites from using the same value in different
           (and incompatible) ways. There is no need for IANA to review
           such assignments and assignments are not generally useful for
           interoperability.

           Examples: Site-specific options in DHCP [DHCP] have
           significance only within a single site.  "X-foo:" header
           lines in email messages.

so it sounds as if the difference between "private" and "experimental" use is 
that private use is for internal use in production and experimental use is for 
internal use when doing experiments, i.e. if you grab a value for private use 
you're probably going to use it consistently in your organization and not 
change its definition arbitrarily, whereas if you grab a value for experimental 
use you may change its definition as a result of your experiments.

So, yes, we could assign a range for it.
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