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The company I am working for is changing the name servers our registrar points to and wants a complete impact analysis in worst case scenario to impacted systems.

I know if we update the TTL's and wait approx 48 hours for replication and then duplicate all entries on old and new name servers update registrar to point to new servers and leave both servers up and running until replication from old to new has occurred there should be no down time but they are interested in worst case.

The worst case scenario is that there is a typo when updating the name server and it points to a none existent name server and is not detected until 48 hours later.

Now their biggest concern is how this will impact Microsoft Office 365 services... specifically how often does Microsoft check for the txt ownership of domain record and is there a possibility all of business could become locked out of O365 etc. because Microsoft checked and decided you no longer own the domain while the name servers couldn't be found. Does any one have experience with that kind of outage and can say if O365 would go down? I can't find specific Microsoft docs on this topic which Business would prefer to see. Has anyone else come across Microsoft docs specifying these details?

axawire
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    "I know if we update the TTL's and wait approx 48 hours for replication" There is no hardcoded value like that in the DNS. If you change nameservers, what counts are the TTL on the `NS` records at the parent of your zone, hence something you don't control, but indeed need to be taken into account. – Patrick Mevzek Aug 19 '22 at 16:40

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how often does Microsoft check for the txt ownership of domain record

Never. The TXT record verification is used one time to verify domain ownership when you add your custom domain to your Office 365 tenant. It's never used after that and can be deleted from your DNS.

If you're concerned about how your name server change might impact your Office 365 services (such as email) then open a support case from your Office 365 tenant and ask them the question. Office 365 support is always free.

joeqwerty
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Worst case is you mess up and don't notice it then you have a outage of whatever you messed up until you fix it and TTL expires. This can be prevented by careful checks and testing the new server before the change-over.

If you can deploy a clone of the old records on the new server worst case is the registrar blocks your update for some unexpected reason, you're then stuck with the old server until the registrar problem is solved.

Actually the worst case is probably that you put the wrong domain name for the new servers, you then have a partial outage lasting until the registrar TTL ends.

Be sure to update the glue records to point to your new DNS.

Jasen
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