Connection to Microsoft services stopped working after enabling VXLAN over IPSEC

Question

Hello everyone,

I'm facing an issue after enabling VXLAN over IPSEC and creating software switches on my FortiGate. I have several scripts that connect to various Microsoft services (e.g., Office 365, Azure), and they were working perfectly before these changes.

However, since enabling VXLAN over IPSEC and configuring the software switch, the scripts are no longer able to connect to the Microsoft services. If I remove the VXLAN from the software switch, the scripts start working again, which suggests that the problem is directly related to the VXLAN configuration or software switch.

Does anyone have suggestions or insights on what to check in the VXLAN over IPSEC or software switch configuration that might be causing these connection issues?

Thanks in advance for your help!

5q46n2te8jPWJY · Accepted Answer

Hi,

Problem solved, I follow instruction of this KB

https://community.fortinet.com/t5/FortiGate/Troubleshooting-Tip-Issues-with-PMTUD-and-VXLAN/ta-p/245153

In my case, correct MMS value is 1330, because of VXLAN encapsulation over IPSEC.

Jean-Philippe_P · Answer

Hello 5q46n2te8jPWJY,   Thank you for the follow up and providing the solution, I am sure it will help a lot of users ;)   Have a great day!

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