Re: Multiple host names for a single server?
On Mon, Jan 7, 2019 at 4:11 PM Andy Smith 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 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
Re: Multiple host names for a single server?
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 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
Re: Multiple host names for a single server?
On Mon, Jan 7, 2019 at 12:26 PM Kushal Kumaran wrote: > Tom Browder writes: > > On Mon, Jan 7, 2019 at 10:24 AM john doe 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
Re: Multiple host names for a single server?
Tom Browder writes: > On Mon, Jan 7, 2019 at 10:24 AM john doe 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
Re: Multiple host names for a single server?
On Mon, Jan 7, 2019 at 10:33 AM Joe 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
Re: Multiple host names for a single server?
On Mon, Jan 7, 2019 at 10:24 AM john doe 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
Re: Multiple host names for a single server?
On Mon, Jan 7, 2019 at 10:20 AM Greg Wooledge 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
Re: Multiple host names for a single server?
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
Re: Multiple host names for a single server?
On Mon, 7 Jan 2019 10:13:03 -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? 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
Re: Multiple host names for a single server?
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
Re: Multiple host names for a single server?
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.
