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Port 27021 Details


known port assignments and vulnerabilities
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Port(s) Protocol Service Details Source
27000-27050 tcp,udp games Ports 27000 to 27050 are typically used by some online games.

Steam (Valve gaming platform) uses these ports:
27000-27015 udp (Steam client game client traffic)
27015-27030 tcp/udp (typically matchmaking and HLTV, also used to download Steam content)
27031 udp, 27036 tcp/udp, and 27037 tcp (incoming for in-home streaming)
3478 udp, 4379 udp, 4380 udp (outbound - Steamworks P2P networking and voice chat)
4380 udp (Steam client)
SG
27020-27039 tcp applications Counter Strike Portforward
27020-27039 tcp applications Day of Defeat Source Portforward
27020-27039 tcp applications Half Life 2 Steam Portforward
27020-27039 tcp applications Half Life Steam Portforward
27020-27050 tcp,udp applications Steam Client Portforward
27010-27344 tcp,udp Unassigned. "Unauthorized Use Known on ports 27017 IANA
7 records found
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External Resources
SANS Internet Storm Center: port 27021

Notes:
Port numbers in computer networking represent communication endpoints. Ports are unsigned 16-bit integers (0-65535) that identify a specific process, or network service. IANA is responsible for internet protocol resources, including the registration of commonly used port numbers for well-known internet services.
Well Known Ports: 0 through 1023.
Registered Ports: 1024 through 49151.
Dynamic/Private : 49152 through 65535.

TCP ports use the Transmission Control Protocol, the most commonly used protocol on the Internet and any TCP/IP network. TCP enables two hosts to establish a connection and exchange streams of data. TCP guarantees delivery of data and that packets will be delivered in the same order in which they were sent. Guaranteed communication/delivery is the key difference between TCP and UDP.

UDP ports use the Datagram Protocol. Like TCP, UDP is used in combination with IP (the Internet Protocol) and facilitates the transmission of datagrams from one computer to applications on another computer, but unlike TCP, UDP is connectionless and does not guarantee reliable communication; it's up to the application that received the message to process any errors and verify correct delivery. UDP is often used with time-sensitive applications, such as audio/video streaming and realtime gaming, where dropping some packets is preferable to waiting for delayed data.

When troubleshooting unknown open ports, it is useful to find exactly what services/processes are listening to them. This can be accomplished in both Windows command prompt and Linux variants using the "netstat -aon" command. We also recommend runnig multiple anti-virus/anti-malware scans to rule out the possibility of active malicious software. For more detailed and personalized help please use our forums.

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