This directive places an upper limit on the size of headers in an HTTP request. When Squid receives an HTTP request with headers that exceed this value, it returns a 413 (Request Entity Too Large) error response. In most cases, request headers are smaller than 512 bytes. This directive exists to catch certain abnormal conditions, such as persistent connection bugs, buffer overflow attempts, and denial-of-service attacks.

Syntax	request_header_max_size size-specification
Default	request_header_max_size 10 KB
Example	request_header_max_size 35 KB
Related	request_body_max_size, reply_body_max_size