Could not verify the server certificate of the gateway. If the issue persists, contact your administrator

[Chibichen1988]

Hello,

I've a case where some users can not connect to our GP gateway. Connection through the portal seems fine but then the client won't connect to the gateway.

We manually reimported the self signed root certificate into the cert store of the client. Also, this issue only happens to users using a specific ISP. All other users using another ISP can connect without issues. Also the users who are affected can connect when they use a hotspot.

Any ideas?

[JayGolf]

Hi @Chibichen1988 ,

It sounds like there may be a problem related to the ISP itself rather than the firewall or GlobalProtect configuration. I would recommend taking a look at your system logs and error code being generated. What do they say? Are these users all at one site with a different ISP? How do you have your gateway configured, is it on the same interface as the portal? Do you have a 1-1 portal/gw configuration? 

[arusharma]

Sounds like MTU issue try reducing the MTU under app settings on portal and test again. The ISP fragmentation issue. 

https://docs.paloaltonetworks.com/globalprotect/5-2/globalprotect-app-new-features/new-features-rele....