Because this is a legacy product, the primary method for acquiring it is through an active Red Hat subscription, which grants access to archive files, or via supported third-party archives. 1. Via Red Hat Customer Portal (Recommended)
Once the .iso file is downloaded, it is crucial to verify its integrity before installation. Verify the ISO (SHA256Sum)
Once you have the rhel-server-5.11-x86_64-dvd.iso , you need to make it bootable.