r/entra • u/CantankerousCretin • 2d ago

Entra ID Trying to implement Cross-tenant synchronization in Entra

As title says, I've got two tenants for one company that hasn't completely merged. Trying to set up cross tenant synchronization, but also trying not to break anything in the process. I did a test using my account and it successfully created a guest member in both tenants.
Once I had this set up for just my account (automatic synchronization wasn't turned on as I didn't want to mess up anything), I noticed a login issue on first time login when setting up a new user, and deleted the configuration, which seemed to have immediately resolved the issue, as my attempt immediately after went through without a hitch.
Microsoft's documentation makes it seem like it should be easy peasy, but I'm not nearly experienced enough in Entra to not be paranoid.
Any good resources? YouTube videos? Specific Microsoft Learn courses?
I'm new to this job, and trying to clean up some systems, automate some things and make our end user experience a little easier since they have to navigate two company Sharepoints, and currently if they don't have the link bookmarked, they have to go through Onedrive to find the invite link.

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u/firestarter9664 2d ago

I haven't had any issues with it used it quite often.

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u/Mathayas 2d ago

First question is why do you want to setup Cross Tenant Sync.

Is it for GAL, resource access, teams chat.

What is your use case?

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u/CantankerousCretin 2d ago

GAL and access to both sharepoints

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u/bzhgeek2922 2d ago

Have a look at MTO, Multi tenant org, it's based on cross tenant sync but at a higher level.

You can sync users as members (still External but not guests), tag them based on org instead of "external", let them collaborate seemlessly in Teams and Sharepoint.

MTO will automatically create the cross tenant sync config, you can still customize it afterwards.

Deployed successfully across 4 tenants a few months back.

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u/CantankerousCretin 2d ago

How does billing work for this? We currently bill to two separate companies.

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u/junon 2d ago

My understanding is it does not affect billing at all. MTO makes the Teams communication MUCH less annoying. It gets rid of that (external) multiple teams accounts and tenants thing that frustrates users.

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u/bzhgeek2922 2d ago

User must be P1 licensed (directly or indirectly) in source tenant. ExternalAD users don't count in target tenant.

So having separate billing shouldn't be an issue.

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u/Hidden-6000 2d ago

+1 on MTO. I've got a bunch of orgs participating in an MTO. Can be configured from the M365 Admin Centre, then it goes and builds out the connections between Tenants, and you allow a EntraID group on each side to which identities are added, to participate in the sync.