[GLLUG] DNS help please

[David Colon]

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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