{"id":39459,"date":"2026-07-09T01:30:25","date_gmt":"2026-07-09T08:30:25","guid":{"rendered":"https:\/\/www.privateinternetaccess.com\/blog\/?p=39459"},"modified":"2026-07-09T01:32:55","modified_gmt":"2026-07-09T08:32:55","slug":"authentication-header","status":"publish","type":"post","link":"https:\/\/www.privateinternetaccess.com\/blog\/authentication-header\/","title":{"rendered":"What Is an Authentication Header? Everything You Need to Know"},"content":{"rendered":"\n

Authentication header is a term that can refer to two different technologies<\/strong>, which often causes confusion. In networking, it usually refers to the Authentication Header (AH) protocol in IPsec. In web applications, people sometimes use the term to refer to the HTTP authorization header.\u00a0<\/p>\n\n\n\n

Understanding the difference between these terms is important because they serve different purposes. In this guide, we\u2019ll explain what an Authentication Header (AH) protocol is, how it works, and how it differs from the HTTP authorization header.<\/p>\n\n\n\n

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Table of Contents<\/h4>\nThe Authentication Header (AH) Explained\n<\/a>
\nHow Do Authentication Headers Work?\n<\/a>
\nHow Authentication Headers Are Used\n<\/a>
\nAuthentication Header Limitations\n<\/a>
\n\nFAQ<\/a>
<\/div>\n\n\n\n\n\n

The Authentication Header (AH) Explained<\/h2>\n\n\n\n

An Authentication Header (AH) is one of the protocols in the <\/strong>Internet Protocol Security (IPsec)<\/strong><\/a> suite.<\/strong> The IPsec suite helps protect IP network communications by providing services such as authentication, integrity checking, and encryption. It\u2019s commonly used to help secure network traffic, including many virtual private network (VPN)<\/a> connections.\u00a0<\/p>\n\n\n\n

The<\/strong> Authentication Header adds a security header to IP packets and supports both IPv4 and IPv6 networks.<\/strong> The AH contains information that allows the receiving device to confirm packet data came from the expected sender and wasn\u2019t modified during transit.<\/p>\n\n\n\n

Authentication Header vs. HTTP Authorization Header<\/h3>\n\n\n\n

The Hypertext Transfer Protocol (HTTP) Authorization header carries authentication credentials<\/strong>, such as a username and password, which clients can send with an HTTP request. Unlike AH, it doesn\u2019t verify packet integrity. Instead, it helps a server verify the identity of the user or application making the request.<\/p>\n\n\n\n

The table below summarizes the main differences between these technologies:<\/p>\n\n\n\n

Authentication Header<\/strong><\/td>HTTP Authorization Header<\/strong><\/td><\/tr>
Part of the IPsec protocol suite<\/td>Part of the HTTP protocol<\/td><\/tr>
Verifies packet authenticity and integrity<\/td>Carries credentials in HTTP requests<\/td><\/tr>
Operates at the network layer<\/td>Operates at the application layer<\/td><\/tr>
Used in IPsec communications<\/td>Used by websites, APIs, and web applications<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

How Do Authentication Headers Work?<\/h2>\n\n\n\n

When a device sends an IP packet with an Authentication Header, it adds additional authentication information before transmission.\u00a0<\/p>\n\n\n\n

\"Flow<\/figure>\n\n\n\n

This information helps the receiving device:<\/p>\n\n\n\n