If this problem is related to this one - https://bugs.launchpad.net/ubuntu/+source/qemu-kvm/+bug/1325560?comments=all - then upgrading the kernel should fix it.
In my case I'm using Ubuntu 14.04 with kernel 3.13 and after upgrading to kernel 3.16, no more connectivity problems.
If this problem is related to this one - https:/ /bugs.launchpad .net/ubuntu/ +source/ qemu-kvm/ +bug/1325560? comments= all - then upgrading the kernel should fix it.
In my case I'm using Ubuntu 14.04 with kernel 3.13 and after upgrading to kernel 3.16, no more connectivity problems.