Quick answer: ARK connection issues: check port 7777 UDP, matching mod list and query port 27015.
If you landed here: ARK shows "Connection failed", "Unable to join" or mod mismatch.
Related
Frequently asked questions (FAQ)
Which ports for ARK dedicated server?
7777 UDP (game), 7778 UDP (raw), 27015 UDP (query). Open all in panel and firewall.
ARK mod mismatch on join?
Server mod list must exactly match client. Install Steam Workshop mods in same order.
ARK ASA vs ASE – same ports?
Similar in principle but ASA uses different server software. Check ports in panel for your game.