IPTables for KVM Host

IPTables for KVM Host

January 26, 2012

By Andrew Galdes

Use the following IPTables rules “/etc/sysconfig/iptables” on a Redhat/CentOS system where this system is a KVM host with KVM guests running. It’s a test script which is known to work. KVM guests often have networking troubles through the fault of the host.

First backup your IPTables firewall:

cp /etc/sysconfig/iptables /etc/sysconfig/iptables.backup

Now apply the following to your “/etc/sysconfig/iptables” file:

*nat
:PREROUTING ACCEPT [661:21364]
:POSTROUTING ACCEPT [58069:3670258]
:OUTPUT ACCEPT [58069:3670258]
-A POSTROUTING -s 192.168.122.0/24 ! -d 192.168.122.0/24 -j MASQUERADE
COMMIT
*filter
:INPUT ACCEPT [1212620:674141323]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [1518464:780474182]
-A INPUT -i virbr0 -p udp -m udp --dport 53 -j ACCEPT
-A INPUT -i virbr0 -p tcp -m tcp --dport 53 -j ACCEPT
-A INPUT -i virbr0 -p udp -m udp --dport 67 -j ACCEPT
-A INPUT -i virbr0 -p tcp -m tcp --dport 67 -j ACCEPT
-A FORWARD -d 192.168.122.0/24 -o virbr0 -m state --state RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -s 192.168.122.0/24 -i virbr0 -j ACCEPT
-A FORWARD -i virbr0 -o virbr0 -j ACCEPT
-A FORWARD -o virbr0 -j REJECT --reject-with icmp-port-unreachable
-A FORWARD -i virbr0 -j REJECT --reject-with icmp-port-unreachable
COMMIT

Don’t forget to restart the IPTables firewall:

/etc/init.d/iptables restart

- See more at: http://agix.com.au/blog/?p=2743#sthash.k8tvF4bp.dpuf