A few questions:

Please describe your network hardware, server hardware , network card and whether it's a dual booting setup. Is the server behind a firewall, if so describe. DNSMASQ in the picture? Are there other computers on the lan?

Also, how did you obtain Knoppix, what version etc.

Are you resinstalling the backed up RHEL and booting it, or reinstalling RHEL without your backed up file system and the problem is there at that point?

The more info you can provide the better.