virtual network with qemu

Nikos Vassiliadis nvass9573 at
Thu May 14 08:29:23 UTC 2009

marco.borsatino at wrote:
> When the installation program asked for information about network configuration, as a 
> first step, I chose DHCP configuration and, as usualy, the network has been set
> like this:
> IP

If I recall correctly qemu has a built-in DHCP server.
That's the one that served you, not a "real" DHCP server
running on your LAN, that is, you are not in any way connected
to the "real" network.

> #qemu -L /usr/local/share/qemu -localtime -net nic,macaddr=00:15:f2:44:2d:01 -net socket,mcast= -hda pc01.img -cdrom /dev/acd0 &
> but the network in the guest system does not work.

It makes sense, that the multicast option will work
between virtual hosts only. That is, it uses multicast
to provide a virtual broadcast domain, which appears to
the host operating system as a ethernet device.

> ifconfig in the guest system tells:
> #ifconfig -a
> ed0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
>   ether 00:15:f2:44:2d:01
>   media: Ethernet 10baseT/UTP <full-duplex>
> plip0: ...
> lo0: ...
> If I try:
> #ping (the gateway)
> all packets are lost. For this reason, I've tryed a static IP configuration like this:
> IP
> gateway
> nameserver
> but the gateway does not respond. So it is useless to try with a second guest system.

No, infact it's the exact opposite. This type of device
will work *only* if you add another virtual system.

To get connected to the "real" network, you must use tap
devices. Correction:
Browsing the qemu's wiki I found out that there is a newer
and simpler approach that I am not familiar with:

So, if you do want internet access, just remove all network
associated options and it will work automagically. If you just
want to connect guest systems together use multicast or socket
or ...

HTH, Nikos

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