[dns-operations] underscores in domain names

[Suzanne Woolf]

On Sep 12, 2017, at 5:53 AM, Jim Reid <jim at rfc1035.com> wrote:

> 
>> On 12 Sep 2017, at 10:19, James Stevens <James.Stevens at jrcs.co.uk> wrote:
>> 
>> It would be impossible to disagree - just interesting to see that
>> underscore in public names is astonishingly common - like SRV records,
>> so I assumed underscore was reasonably well supported.
> 
> It is perfectly legal to use underscores in domain names. They can't be used in hostnames.

This distinction is in fact one of the ones that makes further special-casing characters or label sequences problematic in domain names to be used in the DNS. See https://www.ietf.org/id/draft-lewis-domain-names-09.txt for more than you ever wanted to know about the assorted distinctions and assumptions about domain names embedded in the modern internet.



Suzanne