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Multiple host names for a single server?

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  Multiple host names for a single server? Tom Browder <tom.browder@gmail.com> - 2019-01-07 17:20 +0100
    Re: Multiple host names for a single server? Greg Wooledge <wooledg@eeg.ccf.org> - 2019-01-07 17:30 +0100
      Re: Multiple host names for a single server? Tom Browder <tom.browder@gmail.com> - 2019-01-07 18:50 +0100
    Re: Multiple host names for a single server? john doe <johndoe65534@mail.com> - 2019-01-07 17:30 +0100
      Re: Multiple host names for a single server? Tom Browder <tom.browder@gmail.com> - 2019-01-07 18:50 +0100
        Re: Multiple host names for a single server? Kushal Kumaran <kushal@locationd.net> - 2019-01-07 19:30 +0100
          Re: Multiple host names for a single server? Tom Browder <tom.browder@gmail.com> - 2019-01-07 22:20 +0100
        Re: Multiple host names for a single server? Andy Smith <andy@strugglers.net> - 2019-01-07 23:20 +0100
          Re: Multiple host names for a single server? Tom Browder <tom.browder@gmail.com> - 2019-01-07 23:40 +0100
    Re: Multiple host names for a single server? Joe <joe@jretrading.com> - 2019-01-07 17:40 +0100
      Re: Multiple host names for a single server? Tom Browder <tom.browder@gmail.com> - 2019-01-07 18:50 +0100
    Re: Multiple host names for a single server? Thomas Pircher <thp+debian@p5r.uk> - 2019-01-07 18:00 +0100

#204176 — Multiple host names for a single server?

I would like to use a single server for multiple remote services
including mail, bind dns, OpenStreep tiles, etcs., all with different
subdomain names but sharing the same server and IP.  For example:

  mail.example.com
  ns1.example.com
  tiles.example.com
  ...

I know I can define them with individual A records (with the same IP)
with my domain host provider, but will that cause problems conflicting
with a single physical hostname of, say, "pluto.example2.net"?

In other words, is the physical hostname of any server of any
importance except for logged in users?

Thanks.

-Tom

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#204177

On Mon, Jan 07, 2019 at 10:13:03AM -0600, Tom Browder wrote:
> I would like to use a single server for multiple remote services
> including mail, bind dns, OpenStreep tiles, etcs., all with different
> subdomain names but sharing the same server and IP.  For example:
> 
>   mail.example.com
>   ns1.example.com
>   tiles.example.com
>   ...
> 
> I know I can define them with individual A records (with the same IP)
> with my domain host provider, but will that cause problems conflicting
> with a single physical hostname of, say, "pluto.example2.net"?
> 
> In other words, is the physical hostname of any server of any
> importance except for logged in users?

The actual hostname as set in /etc/hostname does not have to match any
of the various DNS A records, although it will save you some Sanity
points if it does.

The primary purpose of the actual hostname is for you to be able to
identify *which* computer is having a problem.  E.g. if you receive an
email from a machine identifying itself as "www.yourdomain" but you have
three such web servers operating as a round robin, then you will have
to put in some work to figure out which of the three it came from.

But if the email comes from a machine which self-identifies as
"www1.yourdomain", then you have a better idea where to fix the issue.

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#204185

On Mon, Jan 7, 2019 at 10:20 AM Greg Wooledge <wooledg@eeg.ccf.org> wrote:
...
> The primary purpose of the actual hostname is for you to be able to
> identify *which* computer is having a problem.  E.g. if you receive an
> email from a machine identifying itself as "www.yourdomain" but you have
> three such web servers operating as a round robin, then you will have
> to put in some work to figure out which of the three it came from.
>
> But if the email comes from a machine which self-identifies as
> "www1.yourdomain", then you have a better idea where to fix the issue.

Thanks, Greg.

-Tom

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#204178

On 1/7/2019 5:13 PM, Tom Browder wrote:
> I would like to use a single server for multiple remote services
> including mail, bind dns, OpenStreep tiles, etcs., all with different
> subdomain names but sharing the same server and IP.  For example:
> 
>   mail.example.com
>   ns1.example.com
>   tiles.example.com
>   ...
> 
> I know I can define them with individual A records (with the same IP)
> with my domain host provider, but will that cause problems conflicting
> with a single physical hostname of, say, "pluto.example2.net"?
> 
> In other words, is the physical hostname of any server of any
> importance except for logged in users?
> 

Any reasons why you can't use 'cname' record?

-- 
John Doe

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#204182

On Mon, Jan 7, 2019 at 10:24 AM john doe <johndoe65534@mail.com> wrote:
...
> Any reasons why you can't use 'cname' record?

Um, you're right, I should be able to use that now that ACME v2 lets
us use wild cards.

Thanks, "John."

-Tom

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#204190

Tom Browder <tom.browder@gmail.com> writes:

> On Mon, Jan 7, 2019 at 10:24 AM john doe <johndoe65534@mail.com> wrote:
> ...
>> Any reasons why you can't use 'cname' record?
>
> Um, you're right, I should be able to use that now that ACME v2 lets
> us use wild cards.
>

Could you elaborate why the ability to create wildcard SSL certificates
matters for the CNAME-vs-A decision?  They look orthogonal to me.

-- 
regards,
kushal

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#204201

On Mon, Jan 7, 2019 at 12:26 PM Kushal Kumaran <kushal@locationd.net> wrote:
> Tom Browder <tom.browder@gmail.com> writes:
> > On Mon, Jan 7, 2019 at 10:24 AM john doe <johndoe65534@mail.com> wrote:
> > ...
> >> Any reasons why you can't use 'cname' record?
> >
> > Um, you're right, I should be able to use that now that ACME v2 lets
> > us use wild cards.
>
> Could you elaborate why the ability to create wildcard SSL certificates
> matters for the CNAME-vs-A decision?  They look orthogonal to me.

Hm, I think you're correct, Kushal. I was thinking about my crude
domain management tools and got careless in my OP.

Thanks for pointing that out!

-Tom

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#204203

Hi Tom,

On Mon, Jan 07, 2019 at 11:42:28AM -0600, Tom Browder wrote:
> On Mon, Jan 7, 2019 at 10:24 AM john doe <johndoe65534@mail.com> wrote:
> > Any reasons why you can't use 'cname' record?
> 
> Um, you're right

Though do note that the right hand side of MX and NS records should
not point to a CNAME alias (RFC 2181 §10.3)¹. Your examples included
"mail" and "ns1" which often feature in MX and NS records.

Cheers,
Andy

¹ Thought they often end up working anyway, contrary to RFCs.

-- 
https://bitfolk.com/ -- No-nonsense VPS hosting

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#204204

On Mon, Jan 7, 2019 at 4:11 PM Andy Smith <andy@strugglers.net> wrote:> Hi Tom,
> On Mon, Jan 07, 2019 at 11:42:28AM -0600, Tom Browder wrote:
> > On Mon, Jan 7, 2019 at 10:24 AM john doe <johndoe65534@mail.com> wrote:
> > > Any reasons why you can't use 'cname' record?
> >
> > Um, you're right
>
> Though do note that the right hand side of MX and NS records should
> not point to a CNAME alias (RFC 2181 ง10.3)น. Your examples included
> "mail" and "ns1" which often feature in MX and NS records.
...
> น Thought they often end up working anyway, contrary to RFCs.

Thanks, Andy. This has always been a confusing area for me.  When I
get a "practice" mail and dns setup ready I will check back here with
specifics and see what all respondents think.

Best regards,

-Tom

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#204179

On Mon, 7 Jan 2019 10:13:03 -0600
Tom Browder <tom.browder@gmail.com> wrote:

> I would like to use a single server for multiple remote services
> including mail, bind dns, OpenStreep tiles, etcs., all with different
> subdomain names but sharing the same server and IP.  For example:
> 
>   mail.example.com
>   ns1.example.com
>   tiles.example.com
>   ...
> 
> I know I can define them with individual A records (with the same IP)
> with my domain host provider, but will that cause problems conflicting
> with a single physical hostname of, say, "pluto.example2.net"?
> 
> In other words, is the physical hostname of any server of any
> importance except for logged in users?

In general, no. I wouldn't like to assert that there is no server
software that cares what the computer hostname is, but the vast majority
certainly doesn't. Email servers in particular can host a number of
domains, and the HELO hostname returned for each can be configured and
is independent of the machine hostname. Apache2 will handle multiple
domains and can be configured to respond differently according to the
domain name given to it in the URL.

In general you're right, it's just a matter of multiple A records. In
the case of a mail server, the A record used for mail must have a
complementary PTR record at your ISP, but this is not a matter of
whether your mail server works, but whether other mail servers will
accept mail from it.

-- 
Joe

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#204183

On Mon, Jan 7, 2019 at 10:33 AM Joe <joe@jretrading.com> wrote:
...
> In general you're right, it's just a matter of multiple A records. In
> the case of a mail server, the A record used for mail must have a
> complementary PTR record at your ISP, but this is not a matter of
> whether your mail server works, but whether other mail servers will
> accept mail from it.

Thanks, Joe.

-Tom

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#204180

Tom Browder wrote:
> I know I can define them with individual A records (with the same IP)
> with my domain host provider, but will that cause problems conflicting
> with a single physical hostname of, say, "pluto.example2.net"?

Depends on the service. For SMTP, some servers check that results of a
forward and reverse DNS lookup match. See e.g.:

https://mxtoolbox.com/problem/smtp/smtp-reverse-dns-mismatch

You probably want to configure the SMTP service on the machine to use
the DNS PTR name of your public IP address in the EHLO message (e.g. the
myhostname setting in Postfix).

For other services you could consider CNAME records, as John Doe
suggests.

Thomas

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