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I believe this question has been answered a 100 times before, but I'm almost sure that I'm searching into the wrong direction. My desired setup is the following:

I have a virtual host using KVM and libvirt. I have a simple 192.168.1.0/24 home network, which I would like to extend by a server network. I will use 192.168.12.0/24 for the new network. But since there will be a few servers still running in the normal network, I added a virtual network to libvirt. Basicly I would like to route between br0(which is a bridge to eth0) and virbr0(which is the virtual network interface).I have tried to route the traffic using iptables and I have managed it to gain access to the network using these commands

iptables -I FORWARD -d 192.168.12.0/24 -s 0.0.0.0/0 -j ACCEPT
iptables -I FORWARD -s 192.168.12.0/24 -d 0.0.0.0/0 -j ACCEPT
iptables -I FORWARD -s 192.168.1.0/24 -d 0.0.0.0/0 -j ACCEPT
iptables -I FORWARD -d 192.168.1.0/24 -s 0.0.0.0/0 -j ACCEPT

Could someone show me the right direction?

EDIT 1: Thanks for your answers. I completely forgot about the kernel rules and applied them. I am now able to ping the machine from the 192.168.1.0/24 network and vice versa. But I unfortunately am not able to connect via ssh to this machine neither is it possible to ping anything else then 192.168.1.0/24 (and its origin network of course). The "core" router is properly configured, to route anything to the server network, to the kvm hypervisor.

I also thought about the bridge as routed interface, and I added a new interface (eth0:1) which is now my "outside" interface, but this also doesn't change anything.

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  • 1
    linuxpoison.blogspot.com/2008/01/…
    – Creek
    Aug 17, 2014 at 2:43
  • I fail to understand the topology and routing configuration. Can you write an example of what is not working, with IP address of machines involved and their routing table?
    – pqnet
    Aug 17, 2014 at 17:12
  • Thanks for your answer. Sorry for being unclear. What works: - Pinging from one to the other network What doesnt work: - Connecting using anything over OSI Layer 4.
    – olifantastic
    Aug 18, 2014 at 13:21

1 Answer 1

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iptables is used for defining a traffic policy. Adding forwarding rules does not enable forwarding. You must set the according sysctl keys, i.e.

sysctl net.ipv4.conf.br0.forwarding=1
sysctl net.ipv4.conf.virbr0.forwarding=1

equivalently, you may also issue

echo 1 > /proc/sys/net/ipv4/conf/br0/forwarding
echo 1 > /proc/sys/net/ipv4/conf/virbr0/forwarding

You may also need (depends on your setup) to add appropriate routing table entries.

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