underscore in A or PTR records

[Mark Andrews]

The SRV and TXT records usage is depending on underscore not being part of a hostname.
The separator in hostname labels is dash.  e.g. my-host.example.net

_ssh._tcp.example.net SRV can be safely deployed because there are no legal hostnames
starting with _ssh and _tcp.

Hostname (and mail domain) syntax is defined by RFC 952 as modified by RFC1123 (allows
labels to start with digits.

PTR records it depends on usage.

Mark

> On 17 Feb 2021, at 19:13, ONRUBIA AVILES Carlos (CCS/MST) <carlos.onrubia.aviles at proximus.com> wrote:
> 
> Hello ,
>  
> I face the following problem  è bind do not accept an A record with underscore:
>  
> Example:     example_try   A    1.2.3.4
>  
>  
> Same for a PTR:
>  
> Example:   1.2.3.4   PTR   example_try
>  
>  
> Is it absolutely forbidden to have in such cases an ‘_’?
> I know that it is possible for SRV or TXT records.
>  
>  
> Thanks in advance to clarify the situation and sorry if this question has already be asked.
>  
> Carlos,
>  
> 
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-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742              INTERNET: marka at isc.org