Port 27015 (Source engine / Steam game servers)

Default game and RCON port of Source engine servers (Counter-Strike, Team Fortress 2, Garry's Mod) and many Steam dedicated servers.

Registered (user) port, 1024-49151 UDPTCP Games Meant to face the internet

What port 27015 is used for

Default game and RCON port of Source engine servers (Counter-Strike, Team Fortress 2, Garry's Mod) and many Steam dedicated servers.

Meant to face the internet. Game queries on UDP can be used for reflection; keep server software updated and use a strong rcon_password.

Port 27015 is in the registered range and has no IANA assignment. The usage above is unofficial but widespread.

Linux: is anything listening on TCP 27015?

sudo ss -tlnp 'sport = :27015'

Linux: UDP 27015

sudo ss -ulnp 'sport = :27015'

Linux / macOS: which process owns the port

sudo lsof -nP -i :27015

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':27015 '

Windows (Command Prompt)

netstat -ano | findstr :27015

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 27015 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 27015

From Windows

Test-NetConnection HOST -Port 27015

UDP probe (no reply does not prove it is closed)

nc -vzu -w 5 HOST 27015

ufw

sudo ufw allow 27015/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 27015 -j ACCEPT

nftables

sudo nft add rule inet filter input tcp dport 27015 accept

Windows Firewall

New-NetFirewallRule -DisplayName 'Allow TCP 27015' -Direction Inbound -Protocol TCP -LocalPort 27015 -Action Allow

ufw

sudo ufw allow 27015/udp

iptables

sudo iptables -A INPUT -p udp --dport 27015 -j ACCEPT

nftables

sudo nft add rule inet filter input udp dport 27015 accept

Windows Firewall

New-NetFirewallRule -DisplayName 'Allow UDP 27015' -Direction Inbound -Protocol UDP -LocalPort 27015 -Action Allow

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.