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---
title: ALPN
slug: Glossary/ALPN
page-type: glossary-definition
---
{{GlossarySidebar}}
**Application-Layer Protocol Negotiation** (**ALPN**) is a {{Glossary("TLS")}} extension (defined in [RFC 7301](https://www.rfc-editor.org/rfc/rfc7301)) for identifying what application-layer protocol is negotiating the encrypted connection, without requiring additional round trips to do so.
| Protocol | Identification sequence |
| ----------------------------------------- | ------------------------------------------------------ |
| {{Glossary("HTTP", "HTTP/1.1")}} | `0x68 0x74 0x74 0x70 0x2F 0x31 0x2E 0x31` ("http/1.1") |
| {{Glossary("HTTP 2", "HTTP/2")}} | `0x68 0x32` ("h2") |
| HTTP/2 over cleartext {{Glossary("TCP")}} | `0x68 0x32 0x63` ("h2c") |
| {{Glossary("HTTP 3", "HTTP/3")}} | `0x68 0x33` ("h3") |
## See also
- [Performance resource timing `nextHopProtocol`](/en-US/docs/Web/API/PerformanceResourceTiming/nextHopProtocol) property
- [PerformanceObserver API](/en-US/docs/Web/API/PerformanceObserver)
- [IANA registered ALPN identifiers](https://www.iana.org/assignments/tls-extensiontype-values/tls-extensiontype-values.xhtml#alpn-protocol-ids)