Re: [Qemu-discuss] changing from net to netdev with vde switches and double nics

[Thomas Huth]

On 29.08.2017 21:22, Paolo wrote:
> 
> ----------------------------------------------------------------------
>> On Tue, 29 Aug 2017 11:48:20 +0200
>> Thomas Huth <address@hidden> wrote:
> [cut]
>> That's interesting, I think you're the first person I know in months or
>> even years who really seems to be using the vlan=x parameter (with x >=
>> 1)...
> 
> I can't see any other way to realize this topology:
>                        
>              Internet---HOST--SambaServer
>                        |    |
>                        |    |
>                   pubNET    prvNET
>                   |         |
>    |--------------          |
>    |                        |
>  NIC0  NIC1-----------------|
>    |    |
>   machine_1                   ....  machine_N        
>> You're right, you can not translate your setup 1:1 to -netdev anymore,
>> since there are no 'vlan's (or rather hubs, since 'vlan' is rather a
>> misnomer here) available with the -netdev parameter.
> 
> This might be a problem for me, as I explain later 
>> Question is: Why do you need it at all? I see your point that you want
>> to have two network cards, but why does each NIC has to be wired to two
>> host networks (vde *and* tap)? Isn't it sufficient if you connect each
>> NIC to one VDE network?
> 
> Easily: by ignorance.

Deja vu ... this is actually one of the reasons why we want to get rid
of this "vlan" stuff in QEMU. Hardly anybody gets it really right, it
mainly causes confusion and mis-configurations.

> Writing that script (about 8 years ago) with almost zero knowledge of 
> networking and difference between tap, vde (and much more stuff), made me 
> rely on a Frankenstein-style patchwork from midnight readings of the various 
> howtos on internet. Quite a mess and a long and painful trial-and-error race. 
> Nor that today I might be regarded as an expert in networking, I didn't 
> progress very much (and it' not my job anyway).
> 
> Back on topic, following your hint, I've tried just know that all I need is 
> vde, and everything works fine:
> 
>  NET0="-net vde,vlan=0,sock=/var/run/vde.ctl00 -net 
> nic,vlan=0,model=rtl8139,macaddr=$NIC0MAC"
>  NET1="-net vde,vlan=1,sock=/var/run/vde.ctl01 -net 
> nic,vlan=1,model=rtl8139,macaddr=$NIC1MAC"
> 
> Now I guess this is impossbile to achieve with netdev?
> How may I tell to qemu that the guest's NIC0 has to be wired to the vde 
> switch vde.ctl00 run on host has, and NIC1 to vde.ctl01?

It should be doable. Could you please try something like this:

 NET0="-netdev vde,id=v0,sock=/var/run/vde.ctl00 -device 
rtl8139,netdev=v0,mac=$NIC0MAC"
 NET1="-netdev vde,id=v1,sock=/var/run/vde.ctl01 -device 
rtl8139,netdev=v1,mac=$NIC1MAC"

I haven't tested it though, so you still might have to tweak it. Run qemu
with "-device rtl8139,?" to see the options of the rtl8139 device.

> Also hubport function is unclear to me. It reproduces the previous vlan 
> concept, but it's left orphan, because no other devices seems to be made 
> aware that hubportN exists, nor they can be wired to it.

You mean "-netdev hubport"? Forget about it, you don't need it. The hubport
is only required if you want to connect a device to a legacy "vlan" hub. In
your case, you should be fine without these legacy "vlan"s.

 HTH,
  Thomas