Why are dots in username & groupname no longer allowed?

[agibson at ptm.com (Adam Gibson)]

Josh Kelley wrote:
> On 1/5/06, Johnny Hughes <mailing-lists@xxxxxxxxxxxx> wrote:
>> BUT, the I think that the real reason that dots should not be allowed in
>> user names is because this doesn't allow dots:
>>
>> RFC 4282 - The Network Access Identifier
>>
>> There is no requirement to follow this for usernames; however, I think
>> we should.
> 
> Unless I'm misreading the RFC, it does allow dots in usernames?
> 
>    nai         =  username
>    nai         =/ "@" realm
>    nai         =/ username "@" realm
> 
>    username    =  dot-string
>    dot-string  =  string
>    dot-string  =/ dot-string "." string

I don't know myself but Fedora Core 4 allows dots in usernames.  useradd 
asdf.adsf under Fedora Core 4 works just fine as well as userdel 
asdf.asdf .  I wonder which direction RHEL will follow in the future 
since Fedora is usually the test ground for newer stuff in RHEL.