We have similar issue but with the same version on both sides. The checks actually works (it seems), but generates a lot of these errors shown below.
### On a server being checked ### # Installed packages: nagios-nrpe-server/focal,focal,now 4.0.0-2ubuntu1 amd64 [installed] # Output from syslog: 2021-09-30 15:50:22 INFO: SSL Socket Shutdown. 2021-09-30 15:50:22 Could not read request from client *IP*, bailing out... 2021-09-30 15:50:22 Error: (use_ssl == true): Request packet version was invalid! ### On the monitor server ### # Installed packages: nagios-nrpe-plugin/focal,now 4.0.0-2ubuntu1 amd64 [installed] nagios-nrpe-server/focal,now 4.0.0-2ubuntu1 amd64 [installed] # Output from syslog: 2021-09-30 15:50:22 Remote *IP* does not support version 3/4 packets -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1888184 Title: nagios-nrpe-server-4 is creating incorrect log spam To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/nagios-nrpe/+bug/1888184/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
