What's the REAL DEAL with Underscores in BIND8.X?

Scott Morizot tmorizot at ccsi.com
Fri Oct 15 22:40:11 UTC 1999


On Fri, 15 Oct 1999, Ray Galuszka wrote:
> On page 77 in Albitz/Liu's DNS & BIND 3rd Edition, the authors state that
> underscores are not allowed in hostnames.  However, on the next page they
> talk about how you can specify either fail, warn or ignore on the
> check-names option.
> 
> I have LOTS of underscores in my BIND4.x environment now and we're migrating
> to BIND8.  I set up our test server to "ignore" on the check-names option
> and the thing is resolving these names with no problem!
> 
> The question is: if I set this ignore option and use underscores in
> hostnames and aliases, what might I break??   It sure beats putting out
> fires later because some server on my network somewhere expects an
> underscore that I changed to a hyphen in a hostname.

Underscores in hostnames have always been illegal per RFC 952.
Versions of BIND before about 4.9.3 simply didn't enforce the
requirement at all.  (Actually, BIND 4.8 pretty much accepted
anything.)

Allowing underscores will cause a problem with any software or
device that expects names to be compliant with RFC952.  Since
you apparently aren't having a problem now, you may not have
any at the moment.

The long-term solution is to rename the systems using hyphens
instead of underscores and create aliases with the underscore.
Then you can age the aliases off your DNS gradually over time.

Scott




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