Exam MS-720 topic 3 question 18 discussion

Actual exam question from Microsoft's MS-720

Question #: 18
Topic #: 3

You have a Microsoft Teams Phone deployment.
You are deploying Direct Routing.
All users have a SIP URI in the format of [email protected]. The Session Border Controller (SBC) is named sbc.voice.contoso.com.
When troubleshooting errors on the SBC, you receive the warning shown in the following exhibit.

What is a possible cause of the issue?

A. Media bypass is disabled on the SBC.
B. Microsoft 365 Phone System licenses are not assigned to the users.
C. The certificate does not match the FQDN of the SBC.
D. TLS 1.2 is enabled on the SBC.

Show Suggested Answer

Suggested Answer: C 🗳️
SBC connectivity issues.
When you set up Direct Routing, you might experience the following Session Border Controller (SBC) connectivity issues:
Session Initiation Protocol (SIP) options are not received.
Transport Layer Security (TLS) connections problems occur.
The SBC doesn't respond.
The SBC is marked as inactive in the Teams Admin portal.
Such issues are most likely caused by either or both of the following conditions:
A TLS certificate experiences problems.
An SBC is not configured correctly for Direct Routing.
Note: Overview of the SIP options process
* The SBC sends a TLS connection request that includes a TLS certificate to the SIP proxy server Fully Qualified Domain Name (FQDN) (for example, sip.pstnhub.microsoft.com).
* The SIP proxy checks the connection request.
If the request is not valid, the TLS connection is closed and the SIP proxy does not receive SIP options from the SBC.
If the request is valid, the TLS connection is established, and the SBC uses it to send SIP options to the SIP proxy.
* After it receives SIP options, the SIP proxy checks the Record-Route to determine whether the SBC FQDN belongs to a known tenant. If the FQDN information is not detected there, the SIP proxy checks the Contact header.
* If the SBC FQDN is detected and recognized, the SIP proxy sends a 200 OK message by using the same TLS connection.
* The SIP proxy sends SIP options to the SBC FQDN that is listed in the Contact header of the SIP options received from the SBC.
* After receiving SIP options from the SIP proxy, the SBC responds by sending a 200 OK message. This step confirms that the SBC is healthy.
* As the final step, the SBC is marked as Active in the Teams Admin portal.
Reference:
https://docs.microsoft.com/en-us/microsoftteams/troubleshoot/phone-system/direct-routing/sip-options-tls-certificate-issues

by xofowi5140 at Dec. 1, 2022, 5:12 p.m.

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xofowi5140

2 years, 7 months ago

Repeated question.

upvoted 1 times

TheMCT

2 years, 4 months ago

With different correct answer option.

upvoted 2 times

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