Re: [Qemu-discuss] QEMU with pre-created TAP in user mode

[Mike Lovell]

On 07/23/2012 03:33 PM, anatoly techtonik wrote:
> On Tue, Jul 24, 2012 at 12:13 AM, Mike Lovell <address@hidden> wrote:
> > try modifying your command to have '-net user,vlan=0 -net nic,vlan=0 -net
> > nic,vlan=1 -net tap,ifname=tap0,script=no,vlan=1' which just adds the vlan
> > options. you might need to figure out which guest device is in vlan1 with
> > the tap backend. 'info network' on the qemu monitor will tell you. it will
> > probably be the device ending with 57 in the mac address since it would be
> > the second guest network device with the tap.
> Thanks. vlan params helped. Interfaces indeed were mixed, vlan0 mapped
> to eth3 and vlan1 to eth2. Now everything works as expected, but I can
> not say that was a positive user experience. Is it possible to
> simplify this setup by adding more default automation on Qemu side?
> What is the point in creating this hub from all interfaces that
> disrupts network operations with 2+ cards?
> --
> anatoly t.

there are some cases where using multiple network backends is useful. 
i've done it a few times to add the 'dump' back end to a 'vlan' so i can 
examine exactly what traffic was flowing through qemu. it is also useful 
with the 'socket' backends so you can connect multiple together. there 
aren't a lot of use-cases for it. also, using -net to define network 
backends is considered deprecated and its recommended to use -netdev and 
other options. unfortuantely, the documentation all over the web isn't 
updated and so people keep using the -net methods.

networking problems is probably more than half of the traffic on 
qemu-discuss and most of it seems to come from mis-understanding how to 
configure the networking. i spent a lot of time banging my head against 
a wall trying to understand it but finally did and i kind of like it 
now. but until i understood it, i kept cursing it. i would also guess 
that the general answer to 'how to simplify this' is going to be to use 
a management tool like libvirt. i'm not particularly of fan of that 
answer though and why i figured all this stuff out myself.

mike