I have Lubuntu 14.04 LTS with vsftpd and the lamp stack (apache2, etc.) installed. Everything works fine on the LAN. Externally, the services don't acknowledge connection attempts. I can see packets reaching the machine with tcpdump-i eth0 -A, but the machine doesn't send a corresponding ACK. sudo ufw status reports Status:inactive. I don't have any rules configured in iptables; iptables -L has blank output.To make matters more confusing, I can use the external WAN IP assigned to that machine and the hostname from inside the network and connections are successful. To use the WAN IP and hostname externally, I get the same behavior of Ubuntu not sending ACK packets.Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program nametcp        0      0 0.0.0.0:3306            0.0.0.0:*               LISTEN      1494/mysqldtcp        0      0 127.0.1.1:53            0.0.0.0:*               LISTEN      1277/dnsmasqtcp        0      0 0.0.0.0:21              0.0.0.0:*               LISTEN      984/vsftpdtcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      977/sshdtcp        0      0 127.0.0.1:631           0.0.0.0:*               LISTEN      669/cupsdtcp6       0      0 :::80                   :::*                    LISTEN      2175/apache2tcp6       0      0 :::22                   :::*                    LISTEN      977/sshdtcp6       0      0 ::1:631                 :::*                    LISTEN      669/cupsdWithout divulging too much information, the LAN is a class A private 10.x.x.x/22 network. The server has one NIC assigned a static address in the business VLAN. The server's other NIC has a private class C 192.168.x.x/24 static address in the DMZ. An nmap scan of both internal addresses shows identical output, shown below:Nmap scan report for 192.168.x.x/10.x.x.xHost is up (0.0018s latency).Not shown: 996 closed portsPORT     STATE SERVICE21/tcp   open  ftp22/tcp   open  ssh80/tcp   open  http3306/tcp open  mysqlNmap done: 1 IP address (1 host up) scanned in 0.36 secondsA scan on the external IP shows all ports as filtered, meaning nmap didn't get a SYN/ACK or ACK response.Starting Nmap 5.21 ( http://nmap.org ) at 2015-02-10 06:28     UTCHost is up.PORT     STATE    SERVICE21/tcp   filtered ftp22/tcp   filtered ssh80/tcp   filtered http3306/tcp filtered mysql
FTP and WWW services don't acknowledge connections
ubuntu;apache httpd;firewall;vsftpd;lubuntu