Intermittent Azure VPN Connection Issue – “Server did not respond properly to VPN control packets” (AAD Auth / SSL TCP)

Question

Intermittent Azure VPN Connection Issue – “Server did not respond properly to VPN control packets” (AAD Auth / SSL TCP)

Singh, Saurabh 0

Hi Team,

We are experiencing an intermittent issue while connecting to Azure VPN Client, where users encounter the following error:

“Server did not respond properly to VPN control packets.”

Scenario

Issue is intermittent (not consistently reproducible)
Affects multiple users and devices
Occurs across multiple VPN profiles (Dev and Prod environments)

VPN Configuration Details

Authentication:

Azure Active Directory (AAD) based authentication
Cached sign-in enabled
Group token disabled

Protocol:

SSL VPN
Transport Protocol: TCP

VPN Client Profile Type:

Azure VPN Client (XML-based profile)

Server Validation:

Certificate-based validation (hash-based)

Observations

VPN connects successfully at times, but fails intermittently with the above error
Issue is seen across different environments, so it does not appear environment-specific
No consistent correlation with user, device, or network type has been identified so far

Troubleshooting Performed

We have already tried the following based on Microsoft guidance:

Clearing saved credentials / account cache

Helps temporarily

Issue reoccurs after some time

System time synchronization

  - Ensured correct time sync with NTP
  
  
     - Also temporarily mitigates the issue
  
     
     **Re-importing VPN profiles**
  
     
        - No permanent resolution
  
        
        **Testing across networks**
  
        
           - Reproduced across different ISPs
  ```---

Impact

Users are intermittently unable to connect to Azure resources
Causes disruption in daily operations due to repeated connection retries

Questions / Assistance Required

What could be causing intermittent VPN control packet response issues in Azure VPN Client with AAD authentication?
Are there any known issues with SSL (TCP) transport in such scenarios?
Could this be related to:
Token expiration / AAD authentication flow?
Azure VPN Gateway behavior?
Client-side cache/session issues?
- Network middleboxes/firewall interference?

Venkatesan S 8,490 Reputation points Microsoft External Staff Moderator

2026-06-04T23:37:16.0066667+00:00
Hi Singh, Saurabh,

Thanks for reaching out in Microsoft Q&A forum,

Based on the information provided, the intermittent "Server did not respond properly to VPN control packets" error cannot be conclusively linked to a single root cause. While Entra ID (Azure AD) token or credential cache issues remain a possibility, the fact that the issue affects multiple users, devices, and VPN profiles across both Dev and Prod environments suggests that it is unlikely to be caused solely by an expired token or a corrupted local profile.

The observed behavior is more consistent with an intermittent issue occurring during the connection establishment process between the Azure VPN Client and the Azure VPN Gateway. Since the VPN connection succeeds at times and fails at others, the issue may be related to communication interruptions rather than a permanent configuration problem.

Possible contributing factors include:

Intermittent communication issues between the Azure VPN Client and Azure VPN Gateway.

Client-side session or authentication cache issues.

Network devices such as firewalls, proxies, or SSL inspection appliances interfering with VPN traffic.

Temporary Azure VPN Gateway responsiveness or backend service issues.

Entra ID authentication flow or Conditional Access policy-related interruptions.

The fact that clearing saved credentials and synchronizing system time temporarily improves the situation may indicate that authentication or session state plays a role. However, this alone is not sufficient to conclude that refresh token expiration is the primary cause, especially given the broad impact across multiple users and environments.

To further isolate the issue, it would be beneficial to review:

Azure VPN Client logs from affected devices.

Azure VPN Gateway diagnostic logs.

Entra ID sign-in logs during the failure window.

Windows RasClient and Schannel logs for authentication or TLS-related errors.

Official Microsoft documentation:

Troubleshoot Azure VPN Client: https://learn.microsoft.com/en-us/troubleshoot/azure/vpn-gateway/troubleshoot-azure-vpn-client

Troubleshoot Point-to-Site Connection Problems: https://learn.microsoft.com/en-us/troubleshoot/azure/vpn-gateway/vpn-gateway-troubleshoot-vpn-point-to-site-connection-problems

Q&A on This Error: https://learn.microsoft.com/en-us/answers/questions/1658973/server-did-not-respond-properly-to-vpn-control-pac

Q&A on Token Refresh: https://learn.microsoft.com/en-us/answers/questions/5836928/azure-vpn-connection-disconnects

Kindly let us know if the above helps or you need further assistance on this issue.

Please “up-vote” wherever the information provided helps you, this can be beneficial to other community members.

1 answer

Your answer

Answer 1

Hi Saurabh, the "Server did not respond properly to VPN control packets" error shown is almost certainly an Entra ID authentication token expiration or clock-skew issue clashing with your SSL TCP transport. Because TCP requires strict packet ordering, any slight delay while checking your AAD token or CRL causes the gateway to drop the handshake entirely. Since clearing caches and resetting NTP only offer temporary relief, your best long-term fixes are switching the VPN protocol to UDP (OpenVPN) to bypass TCP packet-drop sensitivity, checking your Entra Conditional Access sign-in frequency policies for aggressive token expiration limits, or verifying that your Azure VPN Gateway SKU isn't hitting resource limits during user spikes.

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Intermittent Azure VPN Connection Issue – “Server did not respond properly to VPN control packets” (AAD Auth / SSL TCP)

Scenario

VPN Configuration Details

Observations

Troubleshooting Performed

Impact

Questions / Assistance Required

1 answer

Your answer