[CentOS] VSFTPD passive mode is not working

I have Centos 5.7 64bit; I have installed vsftpd as standalone service and using it for two years now with no problem. Suddenly; only it works with active mode. The passive mode stops working and gives time out. Firewall is disabled and SELinux is set to permissive.

I ran tcpdump and I noticed that only first three packets reached the FTP for passive mode and no more packets on other ports

# lsmod | grep conntrack

ip_conntrack_ftp       41361  1 ip_nat_ftp ip_conntrack_netbios_ns    36033  0 ip_conntrack           91621  5 ip_nat_ftp,ip_nat,ip_conntrack_ftp,ip_conntrack_netbios_ns,xt_state nfnetlink              40457  2 ip_nat,ip_conntrack

Any suggestion?

Eng. Fawzy Ibrahim Linux Systems Administrator