If you have something like pfsense sitting between your network and the internet with suricata installed, then i would check the logs, to see if yum traffic has been blocked. Otherwise what @davidep said, setting the gateway and external DNS is usually an error on my side.
Also what comes to my mind is possibly an ip conflict on your LAN. I have a box, where if i install NS in interactive mode, and set a static IP address, for some reason, by the end off the installation it always changes to the same ip address like my gateway has, rendering both unaccessable after a few minute.
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