How to discover your Transport Relay

Hello,

I was looking into how Teams works under the hood and I've viewed a few resources on how Media flow works and how Teams uses Transport Relays. I saw this one video (https://www.youtube.com/watch?v=p8ml3jYt9KI - note: this is not an official Microsoft resource) that talks about how you discover the first Transport Relay using an anycast IP. The video explicitly says you begin by hitting the endpoint 52.113.192.2. When I ran Wireshark on my system, followed by opening my Teams Client, I never saw this endpoint being hit.


There is an official Microsoft Resource that talks about ensuring reachability for certain Microsoft Endpoints (https://docs.microsoft.com/en-us/microsoft-365/enterprise/urls-and-ip-address-ranges?view=o365-worldwide#skype-for-business-online-and-microsoft-teams). I am assuming those IP ranges are what all the Anycast IPs fall under. My question here is:

How does Teams know which Transport Relay to hit when it turns on?

Is there one specific IP? or is it a range of IPs? If its a range of IPs, how does it select one?

Thanks for any advice or links about this topic.

Some resources I looked at that talks about Transport Relays (but doesn't explicitly tell me which one(s) it hits):
https://docs.microsoft.com/en-us/microsoftteams/microsoft-teams-online-call-flows
https://docs.microsoft.com/en-us/microsoft-365/enterprise/urls-and-ip-address-ranges?view=o365-worldwide#skype-for-business-online-and-microsoft-teams
https://tomtalks.blog/2019/06/where-in-the-world-will-my-microsoft-teams-meeting-by-hosted/
https://www.youtube.com/watch?v=1tmHMIlAQdo