Does Netfilter/iptables support "Trigger Port"?

[richard@xxxxxxxxxxxxxxx]

Hi,everyone: 

  Does Netfilter/iptables support "Trigger Port"? How many ALG type does
it support now? Should I modify the source code? Are there any patchs? 

  I'm developing a router on Linux platform that should support "Trigger
port" and ALG. Does someone can give me some hints? 

  Thanks!