Using iptables Modules in Parallels Cloud Server

Filtering network packets on Hardware Nodes running Parallels Cloud Server does not differ from doing so on a standalone Linux server. You can use the standard iptables tool to control how network packets enter, move through, and exit the network stack within the Parallels Cloud Server kernel.

For your reference, below are several resources you can consult to get detailed information on using iptables on Linux servers:

• Red Hat Enterprise Linux 6 Security Guide ( http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Security_Guide/index.html ) contains a section focusing on packet filtering basics and explaining various options available for iptables .
• iptables Tutorial 1.2.2 ( http://www.frozentux.net/iptables-tutorial/iptables-tutorial.html ) explains in great detail how iptables is structured and how it works.

Defining the Basic Set of iptables Modules for Parallels Cloud Server

All iptables modules you plan to use must first be loaded on the Hardware Node. To do this:

1. Specify the desired modules in the IPTABLES_MODULES parameter in the /etc/sysconfig/iptables-config file. For example:

   IPTABLES_MODULES=" ipt_REJECT iptable_filter iptable_mangle xt_length xt_hl xt_tcpmss xt_TCPMSS xt_multipor t xt_limit xt_dscp "

2. Restart the iptables service for the changes to the /etc/sysconfig/iptables-config file to come into effect:

   # service iptables restart

Using conntrack Rules on Parallels Cloud Server Hardware Nodes

By default, conntrack rules are disabled on the Hardware Node to save resources and increase performance when connection tracking is not needed. To enable connection tracking in Parallels Cloud Server, do the following:

1. Make sure that the following modules are added to the IPTABLES_MODULES variable in the /etc/sysconfig/iptables-config configuration file:

To load the modules on Parallels Cloud Server, add them to the IPTABLES_MODULES variable in the /etc/sysconfig/iptables-config configuration file and restart the iptables service.

1. Set the ip_conntrack_disable_ve0 parameter to 0 in the /etc/modprobe.d/parallels.conf file.
2. Restart the iptables service to apply changes:

   # service iptables restart

3. If required, you can check that the conntrack module is enabled with these commands:

   # cat /proc/net/ip_tables_names

   nat

   # iptables –t nat -L

   Chain PREROUTING (policy ACCEPT)

   target prot opt source destination

   Chain POSTROUTING (policy ACCEPT)

   target prot opt source destination

   Chain OUTPUT (policy ACCEPT)

   target prot opt source destination

Limiting the Maximum conntrack Slots for Parallels Cloud Server

To limit the maximum number of conntrack slots allowed on the Hardware Node, set the net.nf_conntrack_max variable. For example:

# sysctl -w net.nf_conntrack_max=500000

The value of net.nf_conntrack_max also restricts the value of net.netfilter.nf_conntrack_max which limits the maximum conntrack slots for each Container on the Hardware Node.