For installing Enterprise Manager 13c, with our host behind a firewall, we had to open some ports.
We came up with the following list, which should be enough.
oauth-e.oracle.com
aru-akam.oracle.com
ccr.oracle.com
login.oracle.com
support.oracle.com
updates.oracle.com
yum.oracle.com
edelivery.oracle.com
Hope this helps for future installs....
