How to identify the TLS version Jira uses when connecting as a client
Platform Notice: Server and Data Center Only - This article only applies to Atlassian products on the server and data center platforms.
When connecting as a client Jira will start the SSL handshake based off the current Java it's using, Java 8 enables TLSv1.1 and TLSv1.2 in client mode and uses TLSv1.2 by default. The initial request from the client (Jira) will go as TLSv1.2 and since TLSv1.2 is backward compatible, if destination responds on TLSv1.1, then they both agree on TLSV1.1 going forward.
Logging and Configuration
You can verify the SSL handshake in Jira logs, on Logging and Profiling please add the package org.apache.http set to DEBUG.
If you wish to restrict TLS versions used by Jira when connecting as a client, you can set the value of the jdk.tls.disabledAlgorithms parameter in <JRE_HOME>/lib/security/java.security.
The current <JRE_HOME> is available at Administration > System > System Support > System Info > java.home. More Info: https://www.java.com/en/configure_crypto.html
Alternatively, you may also add the following startup properties to achieve these settings: