Apf Block Connection, How Can I Check And Fix

I have apf installed on my server and it looks likely be inreachable,

and i try to reboot the server,

after rebooting, i can not connect from my pc to it any more,

i go to console and test,the server can ping and traceroute the out servers,

i think the newwork is online and the afp black the coming connection.

i try to run "apf -f" to stop the apf,

and my friend can connect the server laster.

i think it may be because the apf black the out-coming connection,

now,i need to check why the apf black others and try to fix it and restart the aps,

can anyone teach me how can i do now?

my server os is centos