squid 中的httpd_accel_host 和httpd_accel_port

小小菜

官方网站有这么一段：
Getting transparent caching to work requires the following steps:
i. ___For some operating systems, you have to configure and build a version of Squid which can recognize the hijacked connections and discern the destination addresses. For Linux this seems to work automatically. For BSD-based systems, you probably have to configure squid with the --enable-ipf-transparent option, and you have to configure squid as:

httpd_accel_host virtual
httpd_accel_port 80
httpd_accel_with_proxy on
httpd_accel_uses_host_header on
看了之后不是很明白？在BSD系统下，明明是作透明代理，又不是作加速器怎么还要用到httpd_accel_host 和 httpd_accel_port呢？