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Re: KVM networking.

Sthu Deus (sthu.deus@gmail.com on 2011-11-11 23:23 +0700):
> >Sthu Deus (sthu.deus@gmail.com on 2011-11-08 14:44 +0700):
> >> 1. The bridges take the Internet connections for itself - thus
> >> leaving the host app.s w/o Internet access, probably routing needed
> >> here - but they do not make any specifications for that.
> >> 
> >That sounds weird. What does brctl show? A default setup with these
> >two lines should already work fine:
> >
> >iface br0 inet dhcp
> >	bridge_ports eth0
> >
> >Just remember to leave eth0 unconfigured...
> Then how do host's app.s will get to Internet?

Through the bridge. I can't tell what's missing until you show us your
bridge configuration, if you have any. I'll show my config for

$ ip addr show eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast
master br0 state UNKNOWN qlen 1000
    link/ether 00:17:31:4a:c6:a3 brd ff:ff:ff:ff:ff:ff
$ ip -4 addr show br0
4: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state
    inet scope global br0

Note the "master br0" on the eth0 configuration, and the lack of any IP
addresses. My routing is slightly different, but you can see there are
no routes using eth0 directly:

ladmin@golem:~$ ip -4 route show
default via dev vlan21 dev br0  proto kernel  scope link  src 

> >> 2. As a workstation - it does not provide access from host to the
> >> guest.
> >> 
> >You mean networking access? I've never needed it, but it should work
> >once your host apps have networking access... (just tested: ping
> >between host and vm works fine for me).
> I mean that DHCP of KVM gives Internet access to guest and having no
> interface from host to guest, I can not reach the guest from host. Of
> course, host app.s and guest's app.s - both have Internet connection,
> but not host-guest connection.

I'm not sure exactly what you're trying to do, but KVM only does DHCP
and basic routing with -net user and not with -net tap FAFAIK.

> >> 3. W/ tap - You have seen already the problem - some unknown to me
> >> permission problem - do You know why is it so?
> >> 
> Now it works - regarding the permission problem, but I need the
> interface (tap).
> Of course I can create by root w/:
> ifconfig tap0 up
> route add -host dev tap0
> but I want w/o root.

Then you should consider using -net user instead of -net tap, I think.
I agree that it is slightly weird that you can't configure a tap
interface even when you own it, but it makes sense: you're not just
configuring the tap interface (which you can do from inside the VM),
you're also changing the host's routing table.

> And even w/ root - I still can not get network working between host
> and guest - having configured guest w/:
See my other mail. You can get the network working by using the correct
routes (I hope). But that won't get you internet access from the VM
without either NAT or reconfiguring your modem.

btw I made a mistake in the previous route command: you shouldn't need
to set a gateway, just the "dev tap0" should be enough.


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