From: Gilles (gilles_at_harfang.homelinux.org)
Date: Sun 26 Sep 2004 - 18:14:16 BST
> > iface dummy0 inet static
> > address 192.168.3.1
> > netmask 255.255.255.0
> > broadcast 192.168.3.255
> > gateway 192.168.1.10
> >
> > But, when the interface is brought up, there is an error message:
> >
> > SIOCADDRT: Network is unreachable
> > Failed to bring up dummy0.
>
> ifup fails if any of the calls fails, in this case the route call fails,
> probably you didn't bring up the interface that makes 192.168.1.10
> reachable _before_ you bring up dummy0
I don't know in which order the interfaces are supposed to be brought up, but
in this case "eth0" ("br0", actually) comes before dummy0 in the file.
Also, now all interfaces are configured, I just ran
ifconfig dummy0 down
then
ifup dummy0
and the result is the same.
> > I'm still confused, because I don't understand why routing just works (but
> > probably not as I expect)!
>
> outgoing packages just take the interface that offers a route to the
> destination, the gateway entry in your /etc/network/interfaces is not
> necessary, packages 'originating from dummy0' will go through eth0
> anyways, if they're going to, for example, 192.168.1.20.
> Within the host no routing occurs, routing just decides through which
> interface a packet is sent out (and through which gateway).
>
> hmm... i guess that also explains the stuff below, right?
>
Yes probably, but my original question was: Is it possible to have a virtual
network (i.e. inside the host) that is an "exact" image of a physical one (i.e.
one for which the host would have been the gateway)?
In the latter case, "eth0" on the host (192.168.1.10) would be connected to
the other machine (192.168.1.20), and would have, say, "eth1" connected to the
192.168.3.0 subnet for which it would be the gateway (with address 192.168.3.1).
No machine on the physical 192.168.3.0 subnet would "see" the other nic of its
gateway, whereas here, the vserver (on the virtual 192.168.3.0) sees both
interfaces: "dummy0" (which, I imagined, is the equivalent of the physical "eth1")
and "eth0", the interface to the other network. Why?
Best,
Gilles
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