[Qemu-discuss] macvlan/macvtap: guest/host cannot communicate when network cable is unplugged

[ching]

Hi all,

I try to setup guest network with macvlan, as guest cannot communicate with 
host directly, i try to workaround by configuring host to using a macvlan 
interface

host: Gentoo x64, kernel 3.5.2, qemu-kvm 1.1.1-r1, libvirt 0.9.13
guest: Ubuntu 12.04, kernel 3.4.9, virtio-net

The host is using macvlan (interface name: znet0, bridge mode)

The guest is using macvtap managed by libvirt (interface name: macvtap0, bridge 
mode)


I am facing a strange problem that the guest/host can communicate only when the 
network cable of the ethernet adapter is connected.

Do anyone have similar problem? Am i missing something?



The network config of the host

$ifconfig

macvtap0  Link encap:Ethernet  HWaddr 52:54:xx:xx:xx:xx
          inet6 addr: fe80::xx:xx:xx:xx/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:70 errors:0 dropped:0 overruns:0 frame:0
          TX packets:84 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:500
          RX bytes:9036 (8.8 KiB)  TX bytes:14734 (14.3 KiB)

znet0     Link encap:Ethernet  HWaddr 00:60:xx:xx:xx:xx
          inet addr:192.168.1.2  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: 2002:xx:xx:xx:xx/64 Scope:Global
          inet6 addr: fe80:xx:xx:xx:xx/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:4463190 errors:0 dropped:0 overruns:0 frame:0
          TX packets:12527522 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:3959213697 (3.6 GiB)  TX bytes:18590336476 (17.3 GiB)

$ip -d link show

10: address@hidden: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue 
state UP mode DEFAULT
    link/ether 00:60:xx:xx:xx:xx brd ff:ff:ff:ff:ff:ff
    macvlan  mode bridge
17: address@hidden: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast 
state UNKNOWN mode DEFAULT qlen 500
    link/ether 52:54:xx:xx:xx:xx brd ff:ff:ff:ff:ff:ff
    macvtap  mode bridge

Regards,
ching