[GLLUG] DNS help please

[Tom Taylor]

On 3 June 2014 17:21, David Colon <dcolon at dcolon.org> wrote:

> The simple solution is to turn the TTL of the A and MX records down to a
> low value like 60. When you are ready to cut over, set an MX 0 record
> pointing to the new email server. I wouldn't bother having a second MX
> record pointing to the old server unless you want to use it in the event
> the primary is down or unreachable.
>
> David
> http://tech.dcolon.org
>
>
>
>
> On Tue, Jun 3, 2014 at 11:06 AM, James Roberts <j.roberts at stabilys.com>
> wrote:
>
>> I am really flaky/stale on DNS and so would much appreciate some advice
>> before I shoot myself in the foot - if anyone has a mo.
>>
>> I have a client with multiple *DSL/Cable connections for connection
>> reliability, none of the connections being very reliable because of their
>> location.
>>
>> Their web is hosted by an Asian developer co on Hertzner, mail is
>> self-hosted on a single Linux server running qmail mailfront etc.
>>
>> The have a single A record, and MX, and a PTR at the DSL ISP. This works
>> - but I want to retire that ISP.
>>
>> Their current mail arrangement uses one ADSL connection which we intend
>> to retire as they now have a fast (30Mbps+) cable connection, which I
>> intend to use as the primary connection.
>>
>> *I want to do two things*:
>>
>> 1 Move the email to the other ADSL connection they have as a first step
>>
>> 2 After a day or two of stable working set up the (tested working) cable
>> connection
>>
>> 3 After a suitable settling period enable email in over both the
>> connections.
>>
>> I have thought of various ways of doing this wrong, and I hope two ways
>> of doing it right.
>>
>> The current entry can be thought of as:
>> *
>> theclient.co.uk MX (Mail Exchanger) Priority: 10 mail.theclient.co.uk
>> mail.theclient.co.uk A (Address) (say) ISP 0 000.000.000.000
>> *
>>
>> The secondary existing service is on (say) ISP1 111.111.111.111
>> The new cable service is (say) ISP2 222.222.222.222
>>
>> The transitional step would add a record as follows:
>>
>> *
>> theclient.co.uk MX (Mail Exchanger) Priority: 10 mail.theclient.co.uk
>> mail.theclient.co.uk A (Address) 000.000.000.000
>> mail.theclient.co.uk A (Address) 111.111.111.111
>> *
>>
>> Q1: But is it OK to have a PTR from each ISP back to the same A record?
>>
>>
>> Q2: However, if I want to make email reception failover work over both
>> the ADSL (111...) and the cable (222...), which of these would be best? I
>> think they achieve the same effect, but the B method allows me more control?
>>
>> Method A
>>
>>
>> mail.theclient.co.uk A (Address) 222.222.222.222
>> mail.theclient.co.uk A (Address) 111.111.111.111
>>
>> theclient.co.uk MX (Mail Exchanger) Priority: 10 mail.theclient.co.uk
>>
>> Method B
>> mail.theclient.co.uk A (Address) 111.111.111.111
>> mail2.theclient.co.uk A (Address) 222.222.222.222
>>
>> theclient.co.uk MX (Mail Exchanger) Priority: 5 mail2.theclient.co.uk
>> theclient.co.uk MX (Mail Exchanger) Priority: 10 mail.theclient.co.uk
>>
>> Any comments from the DNS-literate would be appreciated... and don't
>> hesitate to be rude if necessary :)
>>
>> MeJ
>>
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>>
>
>
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PTR records should point to an A record that points back to the IP
otherwise you will upset all kinds of security checks (SSH, paranoid email
servers etc.).  If you have multiple IPs then that will be multiple PTRs
and therefore multiple A records.
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