Re: [Qemu-devel] net packet storms with multiple NICs
Paul Brook wrote: I immediately reproduced the problem locally. It turns out that kvm reflects packets coming from one guest NIC on another guest NIC, and since both are connected to the same bridge we're getting endless packet storm. To a level when kvm process becomes 100% busy and does not respond to anything but `kill -9'. You created a network loop. It is working exactly as expected. Create the same topology with a physical network hub and a pair of NICs and you'll get the same end result. Paul, I know what the result is. But mind you, I talked about something different, namely: why, using obvious way, you get a packet storm/loop instead of a working network. And if that loop is useful in the first place. I've got answers to both already :) Thanks /mjt -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [Qemu-devel] net packet storms with multiple NICs
I immediately reproduced the problem locally. It turns out that kvm reflects packets coming from one guest NIC on another guest NIC, and since both are connected to the same bridge we're getting endless packet storm. To a level when kvm process becomes 100% busy and does not respond to anything but `kill -9'. You created a network loop. It is working exactly as expected. Create the same topology with a physical network hub and a pair of NICs and you'll get the same end result. Paul -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [Qemu-devel] net packet storms with multiple NICs
Mark McLoughlin wrote: On Fri, 2009-10-23 at 20:25 +0400, Michael Tokarev wrote: I've two questions: o what's the intended usage of all-vlan-equal case, when kvm (or qemu) reflects packets from one interface to another? It's what bridge in linux is for, I think. I don't think it's necessarily an intended use-case for the vlan feature o why different -net guest -net host pairs are not getting different vlan= indexes by default, to stop the above-mentioned packet storms right away? I think it's a wise default to assign different pairs to different vlans, by counting -net host and -net guest sequences. With 0.12, we're going to be de-emphasising the vlan feature and instead have NICs directly connected to host backends. The vlan feature will be just another host backend, but optional You'll start guests with e.g.: -netdev tap,id=tap.0 -device virtio-net-pci,netdev=tap.0 Which is not necessarily more friendly to a user, but it lays the foundation to be able to do a config file which in turns could be easily generated from a nic GUI/command line tool. Regards, Anthony Liguori -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
RE: [Qemu-devel] net packet storms with multiple NICs
-Original Message- From: qemu-devel-bounces+chris.krumme=windriver@nongnu.org [mailto:qemu-devel-bounces+chris.krumme=windriver@nongnu.o rg] On Behalf Of Avi Kivity Sent: Sunday, October 25, 2009 9:23 AM To: Mark McLoughlin Cc: Michael Tokarev; qemu-de...@nongnu.org; KVM list Subject: Re: [Qemu-devel] net packet storms with multiple NICs On 10/23/2009 06:43 PM, Mark McLoughlin wrote: On Fri, 2009-10-23 at 20:25 +0400, Michael Tokarev wrote: I've two questions: o what's the intended usage of all-vlan-equal case, when kvm (or qemu) reflects packets from one interface to another? It's what bridge in linux is for, I think. I don't think it's necessarily an intended use-case for the vlan feature Well, it is. vlan=x really means the ethernet segment named x. If you connect all your guest nics to one vlan, you are connecting them all to one ethernet segment, so any packet transmitted on one will be reflected on others. Whether this is a useful feature is another matter, but the code is functioning as expected. Hello, We had one environment where the NIC understood by u-boot and the NIC understood by the kernel where different. We just attached both to the same VLAN. During u-boot one was used for downloading the kernel, then once the kernel booted the other was used. Not ideal, and maybe not important enough to keep the feature around, but it does get used now and again. Thanks Chris -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [Qemu-devel] net packet storms with multiple NICs
On 10/26/2009 03:40 PM, Krumme, Chris wrote: Well, it is. vlan=x really means the ethernet segment named x. If you connect all your guest nics to one vlan, you are connecting them all to one ethernet segment, so any packet transmitted on one will be reflected on others. Whether this is a useful feature is another matter, but the code is functioning as expected. Hello, We had one environment where the NIC understood by u-boot and the NIC understood by the kernel where different. We just attached both to the same VLAN. During u-boot one was used for downloading the kernel, then once the kernel booted the other was used. Not ideal, and maybe not important enough to keep the feature around, but it does get used now and again. You could get the same behaviour by using two different vlans connected to the same bridge. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [Qemu-devel] net packet storms with multiple NICs
On 10/23/2009 06:43 PM, Mark McLoughlin wrote: On Fri, 2009-10-23 at 20:25 +0400, Michael Tokarev wrote: I've two questions: o what's the intended usage of all-vlan-equal case, when kvm (or qemu) reflects packets from one interface to another? It's what bridge in linux is for, I think. I don't think it's necessarily an intended use-case for the vlan feature Well, it is. vlan=x really means the ethernet segment named x. If you connect all your guest nics to one vlan, you are connecting them all to one ethernet segment, so any packet transmitted on one will be reflected on others. Whether this is a useful feature is another matter, but the code is functioning as expected. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [Qemu-devel] net packet storms with multiple NICs
On Fri, 2009-10-23 at 20:25 +0400, Michael Tokarev wrote: I've two questions: o what's the intended usage of all-vlan-equal case, when kvm (or qemu) reflects packets from one interface to another? It's what bridge in linux is for, I think. I don't think it's necessarily an intended use-case for the vlan feature o why different -net guest -net host pairs are not getting different vlan= indexes by default, to stop the above-mentioned packet storms right away? I think it's a wise default to assign different pairs to different vlans, by counting -net host and -net guest sequences. With 0.12, we're going to be de-emphasising the vlan feature and instead have NICs directly connected to host backends. The vlan feature will be just another host backend, but optional You'll start guests with e.g.: -netdev tap,id=tap.0 -device virtio-net-pci,netdev=tap.0 Cheers, Mark. -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
