关于：过滤钩子驱动程序的三个返回值问题

过滤钩子驱动程序的三个返回值，看了半天，依旧没有看明白，哪位高人指点一二？！
谢谢！
? PF_FORWARD
Specifies for the IP filter driver to immediately return the forward response to the IP stack. For local packets, IP forwards them up the stack. If the destination for packets is another computer and routing is enabled, IP routes them accordingly.
? PF_DROP
Specifies for the IP filter driver to immediately return the drop response to the IP stack. IP should drop the packet.
? PF_PASS
Specifies for the IP filter driver to filter packets and return the resulting response to the IP stack. How the IP filter driver proceeds to filter packets is determined by how it was set with the Packet Filtering API.
The filter hook returns this pass response if it determined that it should not process the packet but should allow the IP filter driver to filter the packet.