Given a domain that is hosted and used for email and web, is an A
record for that domain actually required?
That is, if bob.tld is hosted by example.com can you simply have
NS ns1.example.com
NS ns2.example.com
MX mx.example.com
www CNAME www.example.com
Without specifying
A 11.22.33.444
On 9 Jul 2020, at 22:22, @lbutlr <kremels@kreme.com> wrote:
Given a domain that is hosted and used for email and web, is an A record for that domain actually required?
That is, if bob.tld is hosted by example.com can you simply have
NS ns1.example.com
NS ns2.example.com
MX mx.example.com
www CNAME www.example.com
Without specifying
A 11.22.33.444
(I am pretty sure this is *technically* allowed, but is it really OK to do or are there reasons not to do this?)
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From: Anand Buddhdev <anandb@ripe.net>
To: "@lbutlr" <kremels@kreme.com>, bind-users <bind-users@lists.isc.org>
Cc:
Date: Thu, 9 Jul 2020 14:43:04 +0200
Subject: Re: Dumb Question is an A or AAAA record required?
On 09/07/2020 14:21, @lbutlr wrote:
Given a domain that is hosted and used for email and web, is an A
record for that domain actually required?
It's not *required*. But see below.
That is, if bob.tld is hosted by example.com can you simply have
NS ns1.example.com
NS ns2.example.com
MX mx.example.com
www CNAME www.example.com
Without specifying
A 11.22.33.444
These days, many folk try to reach websites by typing just the bare
domain name without the "www" prefix.
If a user types "bob.tld" into a browser, the browser will issue an
address lookup for "bob.tld", causing the resolver to ask for A and AAAA >records for "bob.tld". If you don't have an A record at the zone apex,
the browser will not get back any address and display an error message
for the user. An alert user might try "www.bob.tld" but most users are
likely to just give up.
So while it's not *required* to have an address record at the apex, it's
good practice to have one.
Anand
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On 9 Jul 2020, at 16:06, Matthew Richardson <matthew-l@itconsult.co.uk> wrote:
On a related issues there were (perhaps long ago) issues if the A record for a domain had an SMTP server on it, where email could sometimes be delivered to that A record rather than the MX. I had (again long ago:
10-15 years) actually seen this occur.
Do people think that this problem could still occur these days? What sort
of transient (presumably DNS) failure might cause an SMTP server to deliver to A rather than MX?
Best wishes,
Matthew
------
From: Anand Buddhdev <anandb@ripe.net>
To: "@lbutlr" <kremels@kreme.com>, bind-users <bind-users@lists.isc.org>
Cc:
Date: Thu, 9 Jul 2020 14:43:04 +0200
Subject: Re: Dumb Question is an A or AAAA record required?
On 09/07/2020 14:21, @lbutlr wrote:
Given a domain that is hosted and used for email and web, is an A
record for that domain actually required?
It's not *required*. But see below.
That is, if bob.tld is hosted by example.com can you simply have
NS ns1.example.com
NS ns2.example.com
MX mx.example.com
www CNAME www.example.com
Without specifying
A 11.22.33.444
These days, many folk try to reach websites by typing just the bare
domain name without the "www" prefix.
If a user types "bob.tld" into a browser, the browser will issue an
address lookup for "bob.tld", causing the resolver to ask for A and AAAA
records for "bob.tld". If you don't have an A record at the zone apex,
the browser will not get back any address and display an error message
for the user. An alert user might try "www.bob.tld" but most users are
likely to just give up.
So while it's not *required* to have an address record at the apex, it's
good practice to have one.
Anand
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On a related issues there were (perhaps long ago) issues if the A record
for a domain had an SMTP server on it, where email could sometimes be delivered to that A record rather than the MX. I had (again long ago:
10-15 years) actually seen this occur.
On a related issues there were (perhaps long ago) issues if the A record
for a domain had an SMTP server on it, where email could sometimes be >delivered to that A record rather than the MX. I had (again long ago:
10-15 years) actually seen this occur.
Do people think that this problem could still occur these days? What sort
of transient (presumably DNS) failure might cause an SMTP server to deliver >to A rather than MX?
From: Anand Buddhdev <anandb@ripe.net>
To: Matthew Richardson <matthew-l@itconsult.co.uk>, bind-users <bind-users@lists.isc.org>
Cc:
Date: Thu, 9 Jul 2020 17:06:13 +0200
Subject: Re: Dumb Question is an A or AAAA record required?
On 09/07/2020 16:06, Matthew Richardson wrote:
On a related issues there were (perhaps long ago) issues if the A record
for a domain had an SMTP server on it, where email could sometimes be
delivered to that A record rather than the MX. I had (again long ago:
10-15 years) actually seen this occur.
Note that *delivery* will only happen if that A record were actually >listening on tcp/25 and accepting SMTP connections. No-one should be
opening up the SMTP port on a server meant to serve only HTTP(S)
traffic. Anyone who does that deserves what they get for making such
poor decisions.
Anand
On 10 Jul 2020, at 02:03, Matthew Richardson <matthew-l@itconsult.co.uk> wrote:
My question is raised because of such "poor decisions" by certain web hosting providers (naming no names!) whose provisioning systems require records for both www and the domain root pointing to their systems, and
where those systems DO LISTEN on port 25.
In these modern days, should one be concerned about this for a domain where the MX records point to proper enterprise grade email services? The
problem is that the web hosting provider's poor decision might interfere
with the enterprise email system.
I think Matus may be correct that this is only an issue if the MX query returns NODATA rather than timing out. In the old days (10-15 years ago),
I think a timeout may have triggered the failback from MX to A, but I am
not sure.
Best wishes,
Matthew
------
From: Anand Buddhdev <anandb@ripe.net>
To: Matthew Richardson <matthew-l@itcons
If you don't have an A record at the zone apex, the browser will not
get back any address and display an error message for the user.
| Sysop: | Keyop |
|---|---|
| Location: | Huddersfield, West Yorkshire, UK |
| Users: | 293 |
| Nodes: | 16 (2 / 14) |
| Uptime: | 239:00:24 |
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| Files: | 12,172 |
| Messages: | 5,319,946 |