networking - Potential network identifiers

Question

What are the different identifiers for individual computers on a network that a network has access to?

I am trying to make two computers look 'identical' from the outside, but even after making MAC address and computer names the same, no go.

Is the domain (COMPUTERNAME.domain.goes.here) visible from the network's POV?

Answer 1

This depends a lot on what you mean with that a network has access to.

If you mean a random non-local network and you are using IP, then it should only know your IP.

If you meant the local network and on the same subnet then MAC addresses are also possible identifiers. As a user you normally ignore these. (Compare this with a mobile phone. I want somebodies phone number, not the serial number of his mobile, even though I have access to it if the phone is in the same room).

All of this assume you use IP and Ethernet. Which is an assumption. Not that many people still use ARCnet hardware or SPX instead of IP. But it would still be nice if you could add that to the original post or tag the post.

I am trying to make two computers look 'identical' from the outside, but even after making MAC address and computer names the same, no go.

First two warnings:

1. Two computers with the same MAC can not use the same Ethernet network at the same time. This because the MAC is supposed to be an unique identifier. If two computers use the same MAC and I send an IP packet to one of them both will receive it. And both will react on it.
2. The MAC address is not available outside the local network. Thus is has no influence outside local network and can not be used to identify or confuse identification outside the local network.

Second, and once more assuming TCP/IP, did you give them the same IP?

Is the domain (COMPUTERNAME.domain.goes.here) visible from the network's POV?

I am not sure if this is visible on the local network.

Answer 2

There are many ways to identify a computer, starting with MAC address. Every network interface card (ethernet adapter, wireless adapter, etc) comes with a MAC address. Your computer keeps a table of these MAC addresses and relates them to IP addresses. Open up a command prompt and run:

arp -a

That will print a list of IP addresses and their matching MAC addresses. If your computer doesn't know an IP addresses' MAC address, it will send an ARP request across the entire network asking for that IP to respond with its MAC address.

DNS matches a name to these IP addresses by asking a DNS server for the A record of a particular name. This returns the IP address the computer needs. Try running:

nslookup google.com

You'll first see the name and IP address of your DNS server. Your router receives the DNS server's IP address through DHCP provided by your Internet service provider. Your computer receives the DNS server's address from your router's DHCP service. You'll then see the IP addresses related to that name. Unless you run your own DNS server, you won't be able to query your computers by DNS name.

NBT (NetBIOS over TCP) is what your computer uses to look up an address by 'Computer Name'. It's a little more difficult to explain in a nutshell, try looking it up.

Changing a single variable, such as a MAC address, might not update and propagate through the network like you would think. Lets say computername.domain.com has an A record of 192.168.1.100 and your computer has a record in its ARP table that associates the MAC address 00:11:22:33:44:55 with 192.168.1.100. Changing the MAC address doesn't change the A record on the DNS server, and won't change even change the ARP tables of other computers immediately. This may be why it seems that the computers aren't ever 'identical', yet nothing is functional.