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 name tcp 0 0 0.0.0.0:3306 0.0.0.0:* LISTEN 1494/mysqld tcp 0 0 127.0.1.1:53 0.0.0.0:* LISTEN 1277/dnsmasq tcp 0 0 0.0.0.0:21 0.0.0.0:* LISTEN 984/vsftpd tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 977/sshd tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN 669/cupsd tcp6 0 0 :::80 :::* LISTEN 2175/apache2 tcp6 0 0 :::22 :::* LISTEN 977/sshd tcp6 0 0 ::1:631 :::* LISTEN 669/cupsd
Without 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.x Host is up (0.0018s latency). Not shown: 996 closed ports PORT STATE SERVICE 21/tcp open ftp 22/tcp open ssh 80/tcp open http 3306/tcp open mysql Nmap done: 1 IP address (1 host up) scanned in 0.36 seconds
A 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 UTC Host is up. PORT STATE SERVICE 21/tcp filtered ftp 22/tcp filtered ssh 80/tcp filtered http 3306/tcp filtered mysql