Resolving MX Records without delay (upgrade from ADSL -> Leased Line)

Posted on 2006-05-04
Last Modified: 2008-03-03
Am looking for best way to manage the migration of a client from ADSL to a Leased Line with minimal impact to Email Delivery

They currently have an ADSL line which is not sufficient and want to upgrade to a leased line - the problem being that when they upgrade the MX records will have to be updated and they take 24-72 hours to resolve.

What is the best workaround for this

One solution we were thinking of was to install another NIC card and separate routers and firewalls (temporarily) for both connections until the Migration is complete - is this feasible? the best solution?

Looking forward to hearing your ideas to my first question since becoming a premium member

Paul Cowen
Question by:pcowen
    LVL 26

    Expert Comment

    The best thing to do would be to lower the TTL (time to live) for the MX records to something like 300. Then let those changes propogate for the 72 hours. During this time everything should function like it normally did, but when you change the MX records (after the ttl has propagated) it'll only take 300 seconds (or whatever value you used) for the new MX record to fully propogate through the internet. Once the new records are updated you can change the ttl back to what it was.

    Since the MX records have already been updated there really isnt much they can do. They can since the new records will have already started propagating. I would just let them go and make a note of what I mentioned above for the next customer. Not much email will be lost during this time, almost all email server will try for at least 5 days before returning undelivered mail.
    LVL 104

    Expert Comment

    The way I do this is to prepare well in advance.
    Get a dynamic DNS address, they are free and add it to your existing MX records well before the switch, pointing at your existing MX records.
    Once that has replicated, the DNS change is under your control.

    Make the switch and then change the dynamic DNS address. As long as the original address has nothing on it, then the email should be delivered to the second MX record.
    Get the original record updated with the new IP address.

    Leave both running for a week or so, then get the dynamic DNS address removed.

    Although for what its worth, I actually leave my clients with the dynamic DNS address in the MX on purpose. In the event of a failure I can get it switched to another IP very quickly.


    Author Comment

    Thanks for both your answers - following on from what Simon posted - is it possible to have both the new and old MX records with different weightings then when propogated remove the old MX record and add the secondary MX record?


    LVL 104

    Accepted Solution

    You can do whatever you like with the MX records.

    The key thing is to ensure that there is at least one valid MX record on the DNS records at all times - hence the use of the dynamic DNS address.

    Due to the way that DNS information propagates round the internet, you need to allow 72 hours for everything to be round before making further changes. I will often make changes on a Monday for work that begins on the Friday, and then make further changes on the Monday after the weekend with a view to the DNS changes being completed by the following Friday - so almost two weeks of DNS monitoring.


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