On Mon, Nov 19, 2012 at 08:35:18AM -0500, Rudy Godoy wrote: If this is intended for the reason you've mentioned, it would be better for the packets to be rejected both ways. Marwan

On Mon, Nov 19, 2012 at 12:09:53PM +0530, mallapadi niranjan wrote: The problem is caused by the relative order of the iptables rules for those two networks. When libvirt created virbr1 for the network 192.168.100.0/24 it inserted a couple of iptables rules on the FORWARDING chain for this interface, but it added them before the rules of virbr0 on the same chain. Those rules basically are ordered as follows (at least on my system which I suspect is different from yours since I also had the same problem): 1. Forward packets destined for the interface that are part of an established connection. 2. Forward packets coming from the interface. 3. Forward packets coming from and destined to the same interface (loopback). 4. Reject forwarding anything else to the interface. 5. Reject forwarding anything else from the interface. Since those rules are inserted for every interface libvirt adds in this order, you can only ping from one interface to another if the set of rules for the interface you are pinging from comes before that of the one you're pinging to. Otherwise, rule number 4 of the destination interface will get in the way since iptables matches the packets against the rules in a chain according to their order on it. A possible workaround: iptables-save >/path/to/iptables/dump/file then, edit the file to move all relevant rules that REJECT things on the FORWARDING chain to the end of the chain. then put this command in your rc.local script: cat /path/to/iptables/dump/file | iptables-restore This solution is not reliable though because you will need to update the file containing the rules every time you add a new virtual network or update the iptables rules for some other reason. Also, I hinted before at this problem on the list and someone pointed me that it's a bug, but nobody confirmed. Read my message on this topic with the subject: Inconsistent iptables forwarding rules for virtual networks, to get a clearer picture. Marwan