Can't access ISE 2.6 web gui admin(error: This Connection is Invalid)

[OlegPerepichay9226]

Hi, i have ISE 2.6 working good, no problems for a long time, authentication working etc. I'm not access web gui often, maybe 1 time a week. But yesterday when i try to login to web gui i get this error: (i change my local data to "xxxxxxx")

This Connection is Invalid
A secure connection to 10.x.x.x cannot be established.
Normally, when you try to connect securely, sites will present trusted identification to prove that you are going to the right place. However, this site's identity can't be verified.

Site:	10.x.x.x
Certificate CN:	*.xxx.xxx
Certificate Authority:	Sectigo RSA Domain Validation Secure Server CA
Certificate Validity:	Not Before: May 13 00:00:00 2019 GMT Not After: May 12 23:59:59 2020 GMT
Certificate Chain:	-----BEGIN CERTIFICATE----- MIIF6jCxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

It's not a web-browser error of a certificate, it's an answer from ISE. I was able to login to ssh normally.

Can someone help me with this? how can i login to web gui now or reset this error?

[Kasun Bandara]

maybe incompatibility with web browser supported TLS versions. can you try to access this from firefox with enabling old TLS method support 

[OlegPerepichay9226 · Accepted solution]

no, this is not a web browser problem but you somehow lead me to solution. It's a fortigate firewall between me and ISE and fortigate have a certificate inspection, so it's fortigate give this error and blocks connection. Thanks for your time!

[ahollifield]

https://www.cisco.com/c/en/us/products/collateral/security/identity-services-engine/bulletin-c25-2503911.html