ietf-822
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Re: Mailing List Last Call for 2822 update internet-draft

2007-07-26 22:23:19

Hi Alan,
At 13:48 26-07-2007, Alan Barrett wrote:
It has happened in the past that software vendors have created
message-id algorithms that did not guarantee unique message-ids in the
face of non-unique host names.  The common wisdom has been that it's
better to generate message-id's of the form <${something derived from
a random number, a timestamp, and the non-unique hostname}(_at_)${something
that encodes the software version}.${vendor's domain name}> than to
generate message-id's of the form <${anyhing}(_at_)${non-unique hostname}>.

Having the hostname on the left or on the right in terms of uniqueness would not be much of a difference as you face the same situation when doing a binary comparison of two message-ids. The use of the domain name/IP address on the right is based on the assumption that it guarantees that the message-id is globally unique. That doesn't always hold nowadays with NAT.

The intent behind my suggested wording is to make it more clear to
software vendors that the domain name on the right hand side of the
message-id is allowed to be the vendor's domain name; that it doesn't
have to be the domain name of the host that's running the software, and
that inability to know the domain name of the host is not necessarily a
problem.

The rationale of having the domain name on the right is that it guarantees uniqueness of the left-hand side within the scope of that domain. If there is a recommendation to use the vendor's domain on the right-hand side, it lessens the scope for uniqueness within that domain. If the domain name of the host cannot be determine, an IP address could be used. Your message-id example is good example for generating a unique identifier. You could have the software version and vendor's domain name on the left though.

Regards,
-sm