When you’re configuring Microsoft Teams emergency calling, there are two end-user experiences. One is where Teams automatically establishes where the user is, based on network information that you’ve configured in Teams. The other is where the client depends on the OS location services and/or the user for a physical address.

For Teams to automatically establish your location, there are a number of pieces of network information that are required. The first of these is what Teams calls a “Trusted IP Address”. That’s maybe not the clearest name, but to be fair the name would get pretty huge if it was any more description.

A Trusted IP Address is any of your organizations public IP addresses that are dedicated, typically statically assigned. When a Teams client accesses Teams using one of these public IPs, Teams can trust that your client is inside your network. There are a few key points here:

Dedicated – The address cannot be shared like some cloud security services do, nor can it be dynamic and change at the whim of your ISP. Fixed IP addresses are typical, though we do sometimes see DHCP assigned “fixed” addresses.

Any – Yes any. Configure the entire range in Teams, not just one IP that clients typically use. This saves your bacon should the firewall guys change which IP clients egress from. It also means you’re covered if someone does something weird like plugging a phone into the server VLAN in the server room.

Trusted IP addresses are configured in TAC under Locations, Network Topology, Trusted IPs. If you click add, the dialog looks something like this:

Pretty straight forward! In the description field, put something meaningful to human. This has nothing to do with your location for emergency calling, but something meaningful like I’ve shown above is very helpful once you have more than one Trusted IP range.

If you’re a PowerShell fan, check out New-CsTenantTrustedIPAddress.

Note that your organization may already have assembled a nice list of these addresses in Azure for Named Locations in the MFA/Condition Access settings. You can spot-test if you’ve got an address in your list by having someone in a site browse to https://www.whatismyip.com. If their public IP address isn’t listed as a Trusted IP Address, you should first investigate if it meets the “dedicated” criteria above, then add it to the Trusted IP Address list.

I’ve been asked “If we monitor our dynamic public IP address for changes, can’t we just have a script run to update that in Teams?”. Well yes you could, except there will be a period of time for the IP change to work its way through Teams and down to all of the clients that require it. So, don’t do this. Instead, sites with dynamic public IP addresses will need to use the “work from home” or “External location lookup mode” as it’s more properly called. I’ve already posted a bit about this function, stay tuned for more.