Suggest an editImprove this articleRefine the answer for “Can multiple applications use the same port?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**At any given moment, one port plus one protocol (TCP or UDP) can be occupied by only one application.** This lets the operating system unambiguously know which process to pass incoming data to. **Key point:** a server listening on a port with many clients connecting to it is not multiple applications on one port, but one application with many connections.Shown above the full answer for quick recall.Answer (EN)Image## The basic rule **At any given moment, one port plus one protocol (TCP or UDP) can be occupied by only one application.** This lets the operating system: - unambiguously know - **which process to pass incoming data to** --- ## What this looks like in practice ### TCP (the most common case) - **One server**: - listens on **one port** (for example, 80 or 443) - **Many clients**: - connect to that port - each client uses **its own temporary (ephemeral) port** Important: - the server is one application - the port is one - the connections are many This is **not multiple applications**, but **one application with many connections**. --- ## Why two different applications cannot simply share a port If: - two different applications - listened on the same TCP port the OS: - could not determine - **which application to hand the incoming segment to** So the OS **forbids** this by default. --- ## Exceptions and nuances ### 1. **UDP + special settings** In UDP it is possible: - to allow multiple applications - to listen on one port (through special socket options) But: - this is a rare and specific case - used in special scenarios (for example, multicast) --- ### 2. **Different protocols** TCP and UDP are different port spaces. So: - one application can listen on **TCP 53** - another on **UDP 53** And this is **normal**. --- ### 3. **Different IP addresses** If a server has: - multiple IP addresses then: - different applications can listen - on the same port - but on **different IPs** Example: ``` 192.168.1.10:80 → application A 192.168.1.20:80 → application B ``` --- ## The key idea The OS distinguishes connections by: ``` IP + port + protocol ``` And for TCP connections, by the full pair: ``` (client IP, client port) ↔ (server IP, server port) ```For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.