Fixing “Cannot find registrar pool” error for sipfed.online.lync.com

I was recently setting up hybrid Lync Skype for Business for a customer. This is more properly known as “split-domain” configuration because you share a single SIP namespace across both the on-premises and cloud portions of the infrastructure.

If you’re not familiar with the process, it goes like this:

1. Set up AD FS or whatever other identity federation solution you like.
2. Configure the service to allow federation.
3. Configure the on-premises Lync/SfB servers to allow federation.
4. Turn on federation.
5. Enable your tenant for split-domain operations with Set-CsTenantFederationConfiguration.
6. Start moving users.

Adam Jacobs’ summary is worth reading if you haven’t seen this before, but even without reading it, it seems straightforward enough, right? I found that when I got to step 6 I got a vexing error: “Cannot find Registrar pool. Verify that ‘sipfed.online.lync.com’ is a valid registrar pool.”

I was 100% sure that the registrar pool name was correct and that it existed, so why couldn’t the Move-CsUser cmdlet find it? I spent some fruitless time binging for a solution (note: this is not the same as “binging on beer” or “binging on carbs before my race”); the few hits I found all suggested ensuring that you’d connected to the service with Import-PSSession, which is, as suggestions go, right up there with “make sure it’s plugged in.”

After some experimentation, I finally figured out that step 3 above hadn’t been performed completely; when I ran Get-CsHostingProvider, the EnableSharedAddressSpace and HostsOcsUsers parameters were both set to “false”. I reset them (and the AutodiscoverUrl parameter, also required), and that solved the problem. It’s not clear to me why anyone at Microsoft thought “cannot find registrar pool” would be an appropriate error for this condition; there are distinct error messages for most other problems that might occur (such as trying to move users to the wrong pool) but not here.

Perhaps this breadcrumb will help some future admin who gets the error, or maybe Microsoft will fix it…