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

[ching <lsching17@gmail.com>]

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, ip: 192.168.1.2, bridge mode)

The guest is using macvtap managed by libvirt (interface name: macvtap0, ip: 192.168.1.184, bridge mode, with vhost)


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




The network config of the host

    $ifconfig

    eth0      Link encap:Ethernet  HWaddr f4:6d:xx:xx:xx:xx  
              inet6 addr: fe80::xx:xx:xx:xx/64 Scope:Link
              UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
              RX packets:86507 errors:0 dropped:0 overruns:0 frame:0
              TX packets:55940 errors:0 dropped:0 overruns:0 carrier:0
              collisions:0 txqueuelen:1000
              RX bytes:126005746 (120.1 MiB)  TX bytes:4394225 (4.1 MiB)

    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: znet0@eth0: <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: macvtap0@eth0: <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

libvirt config of the guest network

    <interface type='direct'>
      <mac address='52:54:xx:xx:xx:xx'/>
      <source dev='eth0' mode='bridge'/>
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/>
    </interface>

The network config of the guest

eth0      Link encap:Ethernet  HWaddr 52:54:xx:xx:xx:xx  
          inet addr:192.168.1.184  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: 2002:xx:xx:xx:xxx/64 Scope:Global
          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:25 errors:0 dropped:0 overruns:0 frame:0
          TX packets:66 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:3108 (3.1 KB)  TX bytes:13066 (13.0 KB)

when network cable of host is plugged in

$ ping 192.168.1.184
PING 192.168.1.184 (192.168.1.184) 56(84) bytes of data.
64 bytes from 192.168.1.184: icmp_req=1 ttl=64 time=0.314 ms
64 bytes from 192.168.1.184: icmp_req=2 ttl=64 time=0.253 ms
64 bytes from 192.168.1.184: icmp_req=3 ttl=64 time=0.230 ms


Afterward, i unplugged the network cable to ensure that packet is not routed via external router, but the test seems failed.

$ ping 192.168.1.184
PING 192.168.1.184 (192.168.1.184) 56(84) bytes of data.
>From 192.168.1.2: icmp_seq=10 Destination Host Unreachable
>From 192.168.1.2: icmp_seq=11 Destination Host Unreachable


Do anyone have similar problem? Am i missing something?


Regards,
ching