Suspicious Connections / Attacks Reported by Router Firewall Targeting Plex Server

Server Version#: 1.42.2.10156
Player Version#: n/a

My router’s firewall (Netgear Armor) is reporting (and blocking) connections from IP address 87.251.67.75 (reverse DNS takes me to ns1.rks-hosting.net which is a European ISP).

I’d like to whitelist any bonafied plex.tv related connections and blacklist any others to keep this at bay. Is there documentation on what I can block without affecting normal Plex usage?

These are continuing and seem to be increasing (from different IPs). Anyone have a suggestion on whitelisting? I couldn’t find any documentation for advanced networking/config to prevent unwanted connections.

I don’t understand networking very well,
I am not sure if this answers your question, but you might look at the page
https://support.plex.tv/articles/200931138-troubleshooting-remote-access/

Towards the bottom of this page in the section labelled “IPs being blocked” there is a link to a list of servers that might be used to initiate remote connections.