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Re: [Qemu-devel] QEMU live migration RARP issue

From: Jason Wang
Subject: Re: [Qemu-devel] QEMU live migration RARP issue
Date: Wed, 20 Jul 2016 17:54:52 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.8.0

On 2016年07月20日 17:10, Robin Geuze wrote:
Hey guys,

A few days ago we noticed that some of our VPSes lost network connection after a live migration using QEMU/KVM. We started investigating and noticed that the problem was at least present for guests running FreeBSD, Debian 7 (Linux 3.2.81-1) and some flavors of CentOS. At least Debian 8 (Linux 3.16.7-ckt25-2) was not affected. Everything is using the virtio drivers. We also noted that the problem was not present in QEMU 2.4.0, but was present in QEMU 2.6.0. The configs between both versions of QEMU are identical. We use libvirt 1.3.5 to manage QEMU/KVM (same version on both qemu versions).

After some false starts we managed to reliably reproduce the issue with a Debian 7 VM. What we noticed was that Debian 8 send out gratuitous ARP replies. Debian 7 did not appear to send those. After some further digging we found out that on QEMU 2.4.0 Debian 7 actually send gratuitous RARP packets after a live migration instead of normal ARP packets and that those where not present when migrating on QEMU 2.6.0. We then started narrowing down the responsible commits using git bisect and eventually ended up with the last good commit being d62241eb6da9bd2517f07b3219ba4208b90b4e0d and the last bad commit we tested was 7ef7bc8586fb0d41742a896b532c7afa2bbb7f84. This is a range of 6 commits introducing the NetFilter functionality. We couldn't really pinpoint it more accurately so we decided to email you guys, to see if you can figure out whats up.


Robin Geuze

TransIP BV

Hello, have you tried latest qemu codes?

We recently fixed a grarp emitting issue in

ca1ee3d6b546e841a1b9db413eb8fa09f13a061b ("net: fix qemu_announce_self not emitting packets")


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