[Qemu-devel] User mode network and multiple nics

[Qemu-devel] User mode network and multiple nics

[Cesare Leonardi]

Hi all.

Some days ago i have done some tests using the user mode network stack
with multiple network interfaces and i noticed some strange behaviours
that i would report to you. I use QEMU 0.7.2 under Debian Sid, using
the package provided by the distribution, and the guest OS is Debian
testing.

I've observed the following things using "-nics n":
1) all the networks interfaces are detected correctly during the boot
    phase: eth0, eth1, ... ethn-1, ethn;
2) the DHCP server doesn't work with the first n-1 interfaces but it's
    OK with the last. For example, with "-nics 4" DHCP works only with
    eth3 and not with eth0,1,2 and with "-nics 2" works only with eth1.
    To try out, in the guest system leave all nics unconfigured, then
    launch the DHCP client on each nic separately. For example, lauching
    dhclient 2.0p15 on the first n-1 interfaces, after some wait, it
    terms saying "No DHCPOFFERS received". With ethn works.
3) in general, seems that the network (not only DHCP) doesn't work
    correctly with first n-1 interfaces. Trying to leave all network
    interfaces unconfigured and trying to configure each of them
    individually with IP 10.0.2.20, netmask 255.255.255.0, 10.0.2.2
    as gateway and 10.0.2.3 as DNS:
    - all nics can ping its IP address;
    - only ethn can ping 10.0.2.2, the others gets "Destination host
      unreachable" from the IP of the network card;
    - none of the nics can ping 10.0.2.3: all gets "Destination host
      unreachable" from the IP of the network card, except ethn, that
      doesn't obtain responses (but the name resolution seems to work);
    - only ethn can go out the 10.0.2.x network (internet, for example).

Anyone has experienced such behaviour that appear to me as bug(s)? It's
a known thing (googling around the mailng-list and internet i have
found nothing)?

Cesare.

Re: [Qemu-devel] User mode network and multiple nics

[John R. Hogerhuis]

User Mode networking is a little tricky to understand. Imagine the
restrictions on your implementation if you had to implement full
networking for another entity, but you had to do it as a regular user.
For instance, don't expect ping (ICMP) to work since a regular user
cannot create a raw socket.

I suggest you use tun/tap or vde.

-- John.