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How to telnet into an unknown IP

Hello world,


Here is the situation, I have a serial terminal box (IOLAN black box to be exact). I have no idea what the IP of this box is but I do know it's MAC address. I need to telnet into this box to be able to change configs on it. I have it connected directly to a laptop.

I tried installing wireshark on the laptop in hopes I'd catch a glimpse of the IP address but no luck. I read somewhere about ARP -s but if it does work can someone explain to be how it would work. Wouldn't communications fail once it gets to layer 3 of the stack on the blackbox? Here is the directions that I've gathered from different sources.

An explanation on why this would work would be greatly appreciated and wouldn't this be a security vulnerability? 


If the address is unknown or undefined, the following sets a temporary IP address:
Set the static ARP with the desired IP address (example: by using the hardware address which is printed on the label of the product. Open a command prompt window by going to START> RUN and type CMD and click OK. This will open a DOS window.
Note: In order for the ARP command to work in Windows, the ARP table on the PC must have at least on IP address defined other than its own. Type "ARP -A" at the DOS command prompt to verify that there is at least one entry in the ARP table. If there is on other entry besides the local machine, ping another IP machine on your network to build the ARP table, This has to be a host other that the machine on which you ware working. Once there is at least one other entry in the ARP table, use the following commands to ARP and IP address in the the unit.
A the command prompt, type arp -s followed by the desired IP address and the the MAC address printed on the label of the device, then press ENTER. See example below:
arp -s 00-20-4A-02-64-0B
After entering the above screen and pressing enter, the command prompt will return. Next, open a Telnet connection to port 1. This connection will fail, but the device will change its IP address to the desired one designated in that step.
telnet 1
Once the command prompt returns stating that it could not open the telnet port, open a Telnet connection to port 9999 and set/program the device with all required parameters.
telnet 9999
Note: The temporary IP address is reverted after every power reset of the device. Be sure to log into the device ans store the parameters to make sure the changes are permanent.
Again why would this work?
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