Detecting known computer on public network in BASH

Question

Anybody know of a way through BASH (specifically OSX terminal, but I'd prefer a BASH only solution without OSX' in built functionality) to detect a known computer on a public network (that I am also located on)?

My thought was that since I know the MAC address of the computer I'm trying to find, I could simply resolve that to an IP, but I'm not sure exactly how I would go about resolving a MAC address to a local IP address on the public network using BASH commands.

My goal is to set up a scripted solution that will allow me to set up a desktop icon that when I double click, detects a known computer on the network and its corresponding local IP address, creates an SSH tunnel for VNC, and then opens the screen sharing app through the SSH tunnel. Essentially, double click to open a secure screen sharing connection on a public network with no third party software and only the tools available via BASH and OSX.

All of this happens within the same public wifi network. For example, imagine two people go to the same coffee shop. I want person A to scan for the IP of Person B given that they already know Person B's IP address.

Answer 1

They make something for this called a DNS name. If it's a public server then it more than likely has one. If it doesn't then you're going to want to make your own, if you already have a DNS name in your org then just add a new A record on your DNS server which specifies a new sub domain for that server. In general, public servers all use static IP addresses though so even this isn't really needed. The IP should never change so just use it. If the IP is changing then you're going to need to either install a dynamic dns client on the server which will keep the DNS entry up to date for you automatically or design your own system (possibly a script which keeps your host file(s) updated [I mean the host files on each of your clients; not the server]). Also, there is no need to worry about local IP vs public IP. This is something your router knows how to manage automatically. As long as your routing table is properly setup it'll find the best path to the server. If you have a home router then this will all be handled automatically behind the scenes.

Update

I actually just thought of a good solution which should work. Get a cloud drive like Google Drive. Set it up on both computers to sync correctly. Then have the other pc write a file to the sync folder which contain the local IP:

echo `ifconfig eth0 2>/dev/null|awk '/inet addr:/ {print $2}'|sed 's/addr://'` > /home/user/share/pcname_current_ip

Now you just need to read that file to find the current IP for that computer (as long as they've both synced of course).

Answer 2

Short answer: The most simple thing to do is probably to install on the laptops something like a dynamic DNS update client to keep track of their dynamic IP address when they are not in your Local Network.

Some words more: The problem is that with only the MAC address you are forced to scan a subnet to find an answering machine with that MAC address once you call it's IP address. Other side of the problem is that this IP change each time the remote machine connects to a provider (or the ADSL reset the connection and assign a different IP address).

It's most simple if that machine (the laptop) communicates somehow the current IP. A way to do it to use a dynamic DNS update client. It exist even a Linux daemon ddclient that help with [dynamic ip servers].(http://ubuntuguide.org/wiki/Dynamic_IP_servers)

After that you choose your name (e.g 'myname.AtFreeOrCommercialProvider.org') and enable on the laptop a program to update the IP, it will be enough to do write from the office the above line to know the current IP of the remote machine:

host myname.AtFreeOrCommercialProvider.org  

after you will be able to write it in your script and use as you want.

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More words on the original way The core of your original question is

I know the MAC address of the computer I'm trying to find, I could simply resolve that to an IP, but I'm not sure exactly how I would go about resolving a MAC address to a local IP address on the public network using BASH commands.

To obtain MAC-address from the IP-address you can use,e.g., one of the following method that will give you IP and MAC-address of answering computer in the net:

1. nbtscan, e.g.nbtscan 192.168.1.0-255 will scan the IP address group you specify answering with IP address, NetBIOS Name, Server, User, MAC address. (If 192.168.1.xxx is your local network...)
2. arp with no mode specifier will print the current content of the IPv4 network neighbour table with IP and MAC address.
   From the same family of tools sudo arp-scan --interface=eth0 192.168.0.0/24 if you are using a cable connection, or sudo arp-scan --interface=wlan0 192.168.0.0/24 if you are using a wireless connection...
3. nmap -sP xxx.xxx.xxx.xxx on all your local network addresses and filter them with the known MAC addresses.
4. nmblookup if you know the NetBIOS names...

After that you have on the same line the IP and the MAC:address you can write your script. Some of this tools may need to be installed.

PS> You can know your current IP address from

# if you are using a cable connection on the network ineterface eth0
sbin/ifconfig eth0 | grep -E "inet:" | awk '{print $2}' | sed s/"inet:"//g
# or you are using a wireless connection on the network ineterface wlan0
sbin/ifconfig wlan0 | grep -E "inet:" | awk '{print $2}' | sed s/"inet:"//g

PPs> IMHO it's not so nice or efficient to scan all internet only to know if that specific computer is connected... It is a different case if you connect this computer to a LAN or a virtual private network (with less IP to be scanned it's possible)... :-)

Answer 3

What about setting up your own ad-hoc wireless network on one of the PCs and route the other PCs traffic through it. Secure and no need for third party ip tracking...

Answer 4

The simplest way to accomplish this is with logmein or team viewer. Yes its third party but it would work very simply.