It turns out that all network interfaces in all VMs had the same
Ethernet address (52:54:00:12:34:56) because we didn't specify any
with the macaddr=... option. This can obviously lead to great
confusion. For instance, when a router forwards a packet, it can
actually end up sending the packet to itself because the target
machine has the same Ethernet address (causing a loop until the TTL
expires), while the target *also* receives the packet. It's amazing
anything worked at all, really.
So now we just set the Ethernet addresses to 52:54:00:12:<virtual
network number>:<machine number>.
svn path=/nixos/trunk/; revision=25020
2e38d8cd31