Polycom to MS Teams Authentication Issue?

Occasional Contributor

Polycom to MS Teams Authentication Issue?

Hi Experts,


May I know if anyone here has a knowledge on how the polycom to MS teams works?
We are experiencing issues with desk phones authenticating to Microsoft Team, We had several troubleshooting with ISP and the action that they did to get this work is to set the TCP MSS value on their PE interface facing our CE to 1460...... but the problem occurred again after a few hours and we are seeing the same issue in where desk phone can't authenticate to MS team (Unable to complete the TLV1.2 handshake).


Diagram/Flow attached

From the packet capture on CE Router we are seeing 2 things.
1. RST packet coming from public network (unable to identify since we don't have control)
2. TCP session is working (3 way handshake) however client is sending "Client hello" however no server response.


1. Any idea why after changing the mss value to 1460 the desk phone connection works and suddenly stops after a few hours ?
2. By default the ISP is using the default MSS value which is 536Bytes. What is the recommended value for MSS on the ISP side ?
3. The only value that is being accepted from df ping is 1496. Is it possible that it is causing the issue? Since if the payload is 1460 + 20 + 20 for header the total is 1500 however the MTU allowed up to Microsoft peering is 1496?
4. Packet capture from CE router shows client sending "do not fragment" and the payload size is just 1300+ so means there are still available for additional overhead.. Is there any possibility that additional overhead is added along the way when reaching Microsoft servers which can exceed to the maximum value of 1496?


Thank you

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Valued Contributor

Re: Polycom to MS Teams Authentication Issue?

Okay, first of all, are you talking about a Teams phone (i.e. a Poly CCX), or a 3PIP phone (like a VVX) that is connecting to the Skype for Business bridge? If it's a VVX, are users signing in with a username and password or are they using Web Sign In?


The Microsoft article describing how Teams call flows work is here: Microsoft Teams call flows - Microsoft Teams | Microsoft Docs. However, since the issue you are seeing is with authentication, I doubt this information will be useful.



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