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Well, I'm using a network connection where IPs are provided by DHCP locked with MAC addresses of the machines. As there are a lot of computer and other devices connected, there isn't enough addresses for all of them, so all 256 addresses from 192.168.1.XXX are already reserved for the 256 machines that used network before available addresses finished... Then, when we need to connect another device, we have to clone MAC address of and turn off an old machine to get its IP.

But someday I forgot to turn off the old machine I cloned MAC, so I could connect the new machine and I could navigate on internet in both computers! But there are some issues with that:

  1. You cannot navigate on internet (or do similar network task, as copying files from network shares of other computers) at the same time on both computers. If you do it, both or one of them will not load correctly the page accessed;
  2. You cannot share folders or printer between the machines with the same MAC.

Is it possible to share that internet connection using the same MAC and IP addresses on two or more computers in that way, and fixing issues 1 and 2, using some kind of software or configuring something on computer settings?

Using the same MAC address on more than one machine at same network can damage hardware of them?

PS: I know it is possible to change the network server properties to allow more machines to connect and that I can use a router to share connection between computers on a subnet. I'm asking for a way to do that thing on same situation, because it can be easier to only change MAC addresses on new networks and/or I would like to know how to do it on a superuser way...

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Managing duplicate mac addresses on a network is far more complicated than setting up sub-nets. Your hardware will not suffer from this, but your users and administrators will. "Some kind of software" to accomplish this has already been invented and it's called TCP/IP. Anything other would require you yo manually manage link access (send and receive in turns) between computers sharing the mac and ip addresses. It does not have to be that difficult to hack together, but it's not worth the effort. –  Ярослав Рахматуллин Nov 28 '12 at 18:26

1 Answer 1

You have at least two solutions:


The first one is to use a bigger network range.

You write the 256 addresses from 192.168.1.XXX are already reserved.

That may be your case, but why not just use a bigger netmask and get 511 instead of 255 addresses?

What you have now is:

Network: (in decimal dotted notation) 192    .168     .1         .hostadresses (0-255)
Network: (in binary notation)         1100000.10101000.00000001  .hostadresses (0-255)
Netmask: (in binary notation)         1111111 11111111 11111111   00000000
Network: (in decimal dotted notation) 255    .255      .255       .0

If you change your netmask to 1111111.11111111.11111110.00000000 (255.255.254.0) then you have 9 bits for those IP adresses. Thus you can specify 512 different values. One is needed as broadcast address, the others are all usable.


The second solution is to use more networks.

192.168/16 contains a whole range of IP nummers, from 196.168.0.0 till 192.168.255.255.
You could add a second network (e.g. 192.168.1.x/24) and set up routing between the outside and both networks. That way you can also create a cleaner setup.

(e.g. all servers in 192.168.0.x, all desktops in 192.168.1.x), all guests in 192.168.2.x etc etc)

All that that requites is some knowledge of how TCP/IP and subnetting works. Which is something you really want to know if you are managing a few hundred computers.


Note: cloning a MAC address is a really bad idea. You mention one reason ("and turn off an old machine to get its IP"), but it is a really ugly hack. And it will confuse switches which keep a table of MAC address and know on which port a certain MAC belongs. A switch may relearn this (at the cost of a little bit of performance), but it is really ugly and it will get harder to manage as the number of computers grows

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