Active Directory domain name length

James
James used Ask the Experts™
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I have a customer that has a external domain name which is 23 characters long that they want to use for a new office 365 tenant so as an example domain looks like this 23characters.com . I need to build them a new internal active directory domain and was going to use int.23characters.com but was wondering if a active directory domain name with 23 characters not including the int. or .com is to long ?
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Commented:
It should be fine.  Just don't go beyond 15 in the netbios name (I STRONGLY recommend the netbios name be something VERY VERY SHORT - for example, if the company is "Twenty Three Characters Inc" then the internal NETBIOS name should be "TTC"
JamesSolutions Architect

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Commented:
Great, thanks for that. The company name is 3 words so I can make the netbios name 3 characters to keep it short.

I was thinking of shortening the internal AD name but i thought it was best practice to have the internal AD domain a sub-domain of the external.

Commented:
onpremise domain and azure ad are different things... you can create a domain and sync users ... it sync only UPN and Password which authenticates at office 365 by azure ad..

for detailed guidiance please check the following

https://docs.microsoft.com/en-us/office365/enterprise/prepare-a-non-routable-domain-for-directory-synchronization?redirectSourcePath=%252fen-us%252farticle%252fHow-to-prepare-a-non-routable-domain-such-as-local-domain-for-directory-synchronization-e7968303-c234-46c4-b8b0-b5c93c6d57a7

all the best
Shaun VermaakTechnical Specialist
Awarded 2017
Distinguished Expert 2018

Commented:
You can probably then just add an shorter UPN, change it on users and sync

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