Hi! I just tried out KVM for the first time, and most things work amazingly well!
However I experience strange problems with the networking. I am using kvm command like this: kvm -hda hda.cow -m 512 -smp 1 -k fi -net nic,model=ne2k_pci,macaddr=52:54:01:00:00:02 -net tap I have set up a bridge, br0, which I have added eth0 to. The problem is that large frames doesn't seem to get forwarded correctly from eth0 to tap0. As I don't see this problem when only using the bridge (ie bridging eth0 to eth1), my guess is that there is some mtu difference between the tap0 and eth0 interface. Both eth0 and tap0 (and consequently br0) have an mtu of 1500. 130.100.71.82 is the guest os (Gentoo Linux and Windows 2003 Server tested in this case with the same result). 130.100.71.1 is the default gw on the network eth0 is connected to. First, a ping of size 1468, as seen on tap0: 20:54:25.552524 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 1496) 130.100.71.82 > 130.100.71.1: ICMP echo request, id 4628, seq 1, length 1476 20:54:25.553486 IP (tos 0x0, ttl 64, id 345, offset 0, flags [none], proto ICMP (1), length 1496) 130.100.71.1 > 130.100.71.82: ICMP echo reply, id 4628, seq 1, length 1476 Ok, ping successfull. Then a one byte longer ping, as seen on eth0: 21:00:07.852892 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 1497) 130.100.71.82 > 130.100.71.1: ICMP echo request, id 31764, seq 1, length 1477 21:00:07.853848 IP (tos 0x0, ttl 64, id 362, offset 0, flags [none], proto ICMP (1), length 1497) 130.100.71.1 > 130.100.71.82: ICMP echo reply, id 31764, seq 1, length 1477 So the responce arrives to eth0 ok, however not to tap0: 20:59:18.908282 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 1497) 130.100.71.82 > 130.100.71.1: ICMP echo request, id 27156, seq 1, length 1477 Then, if we step up to 1473 bytes, as seen on eth0: 21:34:37.319976 IP (tos 0x0, ttl 64, id 55481, offset 0, flags [+], proto ICMP (1), length 1500) 130.100.71.82 > 130.100.71.1: ICMP echo request, id 56598, seq 5, length 1480 21:34:37.320129 IP (tos 0x0, ttl 64, id 55481, offset 1480, flags [none], proto ICMP (1), length 21) 130.100.71.82 > 130.100.71.1: icmp 21:34:37.320980 IP (tos 0x0, ttl 64, id 226, offset 0, flags [+], proto ICMP (1), length 1500) 130.100.71.1 > 130.100.71.82: ICMP echo reply, id 56598, seq 5, length 1480 21:34:37.320983 IP (tos 0x0, ttl 64, id 226, offset 1480, flags [none], proto ICMP (1), length 21) 130.100.71.1 > 130.100.71.82: icmp Now the request is fragmented (correctly), but the first (and large) fragment of the responce gets lost in the bridge: 21:39:03.725524 IP (tos 0x0, ttl 64, id 57750, offset 0, flags [+], proto ICMP (1), length 1500) 130.100.71.82 > 130.100.71.1: ICMP echo request, id 13847, seq 1, length 1480 21:39:03.725667 IP (tos 0x0, ttl 64, id 57750, offset 1480, flags [none], proto ICMP (1), length 21) 130.100.71.82 > 130.100.71.1: icmp 21:39:03.726535 IP (tos 0x0, ttl 64, id 2494, offset 1480, flags [none], proto ICMP (1), length 21) 130.100.71.1 > 130.100.71.82: icmp Does anyone have an idea why it does like this, or how I can get around it? I'm using Gentoo Linux amd64 on a Intel Core2 Duo, and kvm-60. I have tried with both kernel 2.6.23 and 2.6.24, with the same result. I have also tried with both ne2k_pci and rtl8139 nics. /Johan Andersson ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
