Hi

Is it expected behaviour that a libvirt NAT-based network is faster than a libvirt routed network?

I would guess that the routed network would be the fastest one in all cases, but I'm seeing the opposite in my setup. On a 100mbit internet connection, the routed network tops at 4mbyte/sec, while the nat-based network goes all the way to 10mbyte/sec. I've spend the last 6 hours on trying to figure out the cause of this, changing settings, reinstalling the system, but the problem persists and I can't find the cause of it.

It is a clean and fairly simple setup: - Clean installation of CentOS 5.5 - Installation of kvm+libvirt+virt-manager+xorg - iptables service disabled - 1 public IP for the host (xxx.yyy.zzz.215) on a /32 subnet with xxx.yyy.zzz.193 as gateway - 3 public IP for the routed network (xxx.yyy.zzz.251-253) on a /26 subnet with the same gateway as the host - 1 virtual machine with either the NAT or the routed libvirt network assigned

I have no networking connection errors or similar, it works perfectly with both the NAT and the routed network, but the routed network is just 2-4 times slower than the NAT one.

Do you have any suggestions of what the problem might be? When I look at the iptables rules generated by libvirt, and the routing table, everything looks fine AFAICT. Traceroute from guest doesn't reveal anything either. Ping times from the two networks are similar, so the main issue seems to be throughput.

Any help or pointers to what I should look at, is highly appreciated... :)

I've copy pasted some of my relevant system configuration into pastebin: http://pastebin.com/jtTrHLqA

Thank you, Kenni