UDP 27021
Synopsis
- UDP port 27021 is used by Valve Steam/Source Engine dedicated game servers, which operate in the documented UDP range 27015–27030 for server traffic and server queries.
- Real-world examples include community/dedicated servers for Counter-Strike 2 (formerly CS:GO), Team Fortress 2, Garry’s Mod, Left 4 Dead 2, and Dota 2.
- The protocol on this port is the Steam/Source server query interface (A2S_INFO/A2S_PLAYER/A2S_RULES) and related game traffic.
- This port (like others in 27015–27030) has been abused for UDP reflection/amplification DDoS attacks against exposed Source-engine servers.
Observed activity
Last 30 days
Detailed chart