4.5.3. Creating Network Packet Filter Rules
Before assigning any iptables rules for FTP service, review the information in Section 4.4.1, “Assigning Firewall Marks” concerning multi-port services and techniques for checking the existing network packet filtering rules.
Below are rules which assign the same firewall mark, 21, to FTP traffic. For these rules to work properly, you must also use the VIRTUAL SERVER subsection of Piranha Configuration Tool to configure a virtual server for port 21 with a value of 21 in the Firewall Mark field. See Section 5.6.1, “The VIRTUAL SERVER Subsection” for details.
The rules for active connections tell the kernel to accept and forward connections coming to the internal floating IP address on port 20 — the FTP data port.
The following iptables command allows the LVS router to accept outgoing connections from the real servers that IPVS does not know about:
/sbin/iptables -t nat -A POSTROUTING -p tcp -s n.n.n.0/24 --sport 20 -j MASQUERADE
In the iptables command, n.n.n should be replaced with the first three values for the floating IP for the NAT interface's internal network interface defined in the GLOBAL SETTINGS panel of Piranha Configuration Tool.
The rules for passive connections assign the appropriate firewall mark to connections coming in from the Internet to the floating IP for the service on a wide range of ports — 10,000 to 20,000.
If you are limiting the port range for passive connections, you must also configure the VSFTP server to use a matching port range. This can be accomplished by adding the following lines to /etc/vsftpd.conf:
pasv_min_port=10000
pasv_max_port=20000
You must also control the address that the server displays to the client for passive FTP connections. In a NAT routed LVS system, add the following line to /etc/vsftpd.conf to override the real server IP address to the VIP, which is what the client sees upon connection. For example:
pasv_address=n.n.n.n
Replace n.n.n.n with the VIP address of the LVS system.
For configuration of other FTP servers, consult the respective documentation.
This range should be a wide enough for most situations; however, you can increase this number to include all available non-secured ports by changing 10000:20000 in the commands below to 1024:65535.
The following iptables commands have the net effect of assigning any traffic addressed to the floating IP on the appropriate ports a firewall mark of 21, which is in turn recognized by IPVS and forwarded appropriately:
/sbin/iptables -t mangle -A PREROUTING -p tcp -d n.n.n.n/32 --dport 21 -j MARK --set-mark 21
/sbin/iptables -t mangle -A PREROUTING -p tcp -d n.n.n.n/32 --dport 10000:20000 -j MARK --set-mark 21
In the iptables commands, n.n.n.n should be replaced with the floating IP for the FTP virtual server defined in the VIRTUAL SERVER subsection of Piranha Configuration Tool.
The commands above take effect immediately, but do not persist through a reboot of the system. To ensure network packet filter settings are restored after a reboot, see Section 4.6, “Saving Network Packet Filter Settings”
Finally, you need to be sure that the appropriate service is set to activate on the proper runlevels. For more on this, refer to Section 3.1, “Configuring Services on the LVS Routers”.