> Subject: Re: Network throughput limits for local VM <-> VM > communication > > Fischer, Anna wrote: > > I am using two bridges, and yes, in theory, the router should be the > only connection between the two guests. However, without VLANs, the tun > interface will pass packets to all tap interfaces. It has to, as it > doesn't know to which one the packet has to go to. It does not look at > packets, it simply copies buffers from userspace to the tap interface > in the kernel. The tap interface then eventually drops the packet, if > the MAC address does not match its own. So packets will not actually go > across both bridges, because the tap interface that should not receive > the packet does drop it. However, it does receive the packet and > processes it to some extend which causes some overhead. As I was told > by someone at KVM/RedHat, this does not happen when using VLANs as then > there will be a direct mapping between any tun<->tap device and so no > packet replication across multiple tap devices. > > > > This only happens if the receiving tap never sends out packets. If the > tap interface does send out packets, the bridge will associate their > MAC > address with that interface, and future packets will only be forwarded > there. > > Is this your scenario? Not sure I understand. As far as I can see the packets are replicated on the tun/tap interface before they actually enter the bridge. So this is not about the bridge learning MAC addresses and flooding frames to unknown destinations. So I think this is different. Anna -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
