[Qemu-discuss] Network connection between hosts drops when using virtio network card

[Bram Klein Gunnewiek]

I am testing some qemu stuff in a local enviroment where I have a 
"cluster" of one virtualbox vm and my bare metal machine (the virtualbox 
vm runs on my machine). I have disabled kvm hardware virtualisation 
(rmmod kvm_intel). I have one single network card in my PC 
(RTL8111/8168/8411) that is configured as a bridge. The virtualbox vm is 
linked to that bridge so the vm gets an IP from my local DHCP server.

This works fine except when I use a virtio network card on a guest 
system. If I do that I loose the connection to my virtualbox vm. I don't 
have much experience with linux networking and bridges but the strange 
thing is that this only happens with virtio network cards. If I use an 
e1000 card in my qemu guest everything works fine. Can someone spot the 
issue or knows where to look? There is nothing helpfull in my kernel logs.

Network configuration:

iface bridge0 inet dhcp
bridge_ports eth1
bridge_stp off
bridge_fd 0

Goes wrong:

sudo qemu-system-x86_64 -daemonize -smp 1 -m 128 -vnc 0.0.0.0:0 \
-netdev tap,id=tap_1,script=no,downscript=no,ifname=net_1_1,vhost=off \
-device 
virtio-net-pci,bootindex=1,id=nic_1,netdev=tap_1,mac=02:16:3E:00:00:01; \
sudo brctl addif bridge0 net_1_1; \
sudo ifconfig net_1_1 0.0.0.0 up;

Works:

sudo qemu-system-x86_64 -daemonize -smp 1 -m 128 -vnc 0.0.0.0:0 \
-netdev tap,id=tap_2,script=no,downscript=no,ifname=net_1_2 \
-device e1000,bootindex=2,id=nic_2,netdev=tap_2,mac=02:16:3E:00:00:02; \
sudo brctl addif bridge0 net_1_2; \
sudo ifconfig net_1_2 0.0.0.0 up;

--
Met vriendelijke groet / Kind regards,
Bram Klein Gunnewiek | Shock Media B.V.

Tel: +31 (0)546 - 714360
Fax: +31 (0)546 - 714361
Web: https://www.shockmedia.nl/