underscore in A or PTR records

Wed Feb 17 08:50:44 UTC 2021

Hello,

Thanks for these clarifications.
The issue we face is that a telecom provider ask us to implement a PTR record with a name like "example_try.net"
We tried this configuration but BIND do not accept it.
The telecom provider complaints we can not make this DNS configuration and that it must be possible (for the moment they do not gave us examples to prove what they say).

So to be clear can we answer to this telecom provider that using a PTR with "_" is not possible and not RFC compliant? Or is there anything I miss?

Thanks in advance for your time.

Carlos,

Sensitivity: Internal Use Only

-----Original Message-----
From: Mark Andrews <marka at isc.org>
Sent: 17 February 2021 09:28
To: ONRUBIA AVILES Carlos (CCS/MST) <carlos.onrubia.aviles at proximus.com>
Cc: bind-users at lists.isc.org
Subject: Re: underscore in A or PTR records

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
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