Debian – Add eth2, eth3 etc. instead of eth1:0, eth1:1 etc

You have multiple interfaces with addresses on the same subnet with similar netmasks. The odds are a different route is being used for different packets, causing confusion. If you look at the output of

ip route show

You've probably got multiple default gateways as a result. For each set of IPs on the same subnet, give one of them the netmask you have, and the rest a netmask of 255.255.255.255. Those other interfaces will then only be used for packets originating or destined for that address and not others on the subnet.

You can see all networking devices by running:

ifconfig -a

Another trick to debugging the ethernet drivers is to look at dmesg:

dmesg|less

You will see each driver loading and creating ethernet devices.

You mention your ethernet device changing to eth2. Did you copy or move the VM? Typically when you make a copy of a VM it will re-create the MAC address so as to not conflict with the former copy. If this happens udev will assign the "new card" another eth* device and save the previous device for the "missing" card. These rules are stored in:

/etc/udev/rules.d/

Typically in a file called ##-persistant-net.rules. You can safely remove the assignments stored in this file and reboot to have the ethernet devices reassigned.