I'm using KVM and libvirt and experience small network freezes on the host and the guests every 2-3 minutes or so. The freezes last 1-2 seconds. The used OS is Ubuntu 10 LTS server edition.
I'm using a standard bridge setup with the host additionally serving as a router for the guests (because the data center always routes the guest IPs to the host). This all works fine except for the occasional network freezes every few minutes. A
mtr trace from external machines reports a packet loss of around 1-2% (for the host and the guests).
I found out that when I disable ip forwarding on the host (/proc/sys/net/ipv4/ip_forward), the freezes do not occur anymore (but the guests then obviously have no network connectivity), so I guess it's a software related problem rather than a hardware issue.
I've tried switching to alternative network drivers in the guests (from virtio to e1000/rtl), disabling our iptables packet filtering, playing around with various network options (turning off/on icmp redirects, among others) but this hasn't changed anything.
Any thoughts and ideas on this are much appreciated.