Would you happen to be using an old operating system like RHEL5? I don't know when the config changed but the Splunk download servers now seem to require that clients have TLS SNI support. That's not really a big deal for newer clients but it doesn't look like this was in the OpenSSL release in RHEL5, as one example. The site seems to insist on HTTPS so you might be stuck scp'ing the file over to your systems unless you want to locate or build a wget or curl binary that's statically-linked to a more recent OpenSSL version. Maybe Splunk will share a non-HTTPS download location!