---
title: 应用层协议协商
slug: Glossary/ALPN
tags:
  - ALPN
  - TLS
translation_of: Glossary/ALPN
---
<p><strong>应用层协议协商</strong>（<strong>Application-Layer Protocol Negotiation</strong>，简称<strong>ALPN</strong>）是 {{Glossary("TLS")}} 的一个扩展，故而应用层协议在协商加密协议的过程中，避免了额外的往返通讯开销。</p>

<table class="standard-table">
 <caption>几个重要的标识符:</caption>
 <thead>
  <tr>
   <th scope="col">协议</th>
   <th scope="col">标识符字节序列</th>
  </tr>
 </thead>
 <tbody>
  <tr>
   <td>{{Glossary("HTTP")}}/1.1</td>
   <td><code>0x68 0x74 0x74 0x70 0x2F 0x31 0x2E 0x31</code> ("http/1.1")</td>
  </tr>
  <tr>
   <td>{{Glossary("HTTP 2", "HTTP/2")}}</td>
   <td><code>0x68 0x32</code> ("h2")</td>
  </tr>
  <tr>
   <td>HTTP/2 over cleartext {{Glossary("TCP")}}</td>
   <td><code>0x68 0x32 0x63</code> ("h2c")</td>
  </tr>
 </tbody>
</table>

<h2 id="Specifications">Specifications</h2>

<table class="standard-table">
 <thead>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Notes</th>
  </tr>
 </thead>
 <tbody>
  <tr>
   <td>{{RFC(7301)}}</td>
   <td><span class="spec-RFC">IETF RFC</span></td>
   <td>初始化定义</td>
  </tr>
 </tbody>
</table>

<h2 id="See_also">See also</h2>

<ul>
 <li><a href="https://www.iana.org/assignments/tls-extensiontype-values/tls-extensiontype-values.xhtml#alpn-protocol-ids">IANA registered ALPN identifiers</a></li>
</ul>