I just got the arduino ethernet shield and I am not sure what to use for the mac address and IP address? Do I use the mac address of my router? Do I use the IP adress that my computer is assigned?
Please help
Thanks
Rico
Do NOT use the Mac address of your router. You will cause many things to stop working in your house.
I suggest finding an old hunk of junk and use its mac address. Every device on the planet is suppose to be unique.
You can make up an IP address, pick something that will never be used on your local lan, addresses are location specific and are re-used everywhere.
example: 192.168.1.234
Even the mac address could be made-up. Reversing a few characters of your router's mac address is a good start.
Thanks a million for the information, I just got the arduino online!! 
If you want to be pedantic:
"Universally administered and locally administered addresses are distinguished by setting the second least significant bit of the most significant byte of the address. If the bit is 0, the address is universally administered. If it is 1, the address is locally administered. The bit is 0 in all OUIs. For example, 02-00-00-00-00-01. The most significant byte is 02h. The binary is 00000010 and the second least significant bit is 1. Therefore, it is a locally administered address." -- MAC address - Wikipedia
So, afaict if your made up MAC starts with 02 it's more "proper" and won't clash with any official one.
--Phil.
I just would like to ad another step I had to do to access my arduino board outside of my personal network for people who may not know!
I have a linksys router, so I had to log onto the router by typing in the address bar: 192.168.0.1 (This address should work for any llinksys router) leave the username blank and type admin for the password. This will work if you did not change the settings. If you did and can not remember just reset the router by pushing the button on the back of the router for 10 seconds and release. Navigate to the applications and gaming tab and fill in the blanks: for example in row one under the application type "Arduino", under start type "80", under End type "80" under Protocol type select "TCP" and under IP address type whatever the last part of your IP address to your board is and then select enable. Now navigate to your Administration tab and the IP address in this list which is the IP address of your router is what you will need to type in the address bar from a remote location to access your board. Hope this helps.
Thanks
Rico Bravo
So, afaict if your made up MAC starts with 02 it's more "proper" and won't clash with any official one.
That's exactly right. That's the purpose of that particular address block.
Ethernet addresses have special blocks, just like IP addresses do. Some are assigned to companies who make hardware, some are for multicast, and some are set aside for user-defined use (the 02-xx-xx-xx-xx-xx block).
Just make sure you don't "make up" the same address if you happen to have two Ethernet shields. Everything assumes that ethernet addresses are unique, and you do not want to try to troubleshoot a network problem involving a duplicate MAC address.
-j
So, afaict if your made up MAC starts with 02 it's more "proper" and won't clash with any official one.
That's exactly right. That's the purpose of that particular address block.
Ethernet addresses have special blocks, just like IP addresses do. Some are assigned to companies who make hardware, some are for multicast, and some are set aside for user-defined use (the 02-xx-xx-xx-xx-xx block).
-j
According to the ieee oui.txt list (http IEEE SA - Registration Authority) That is not completely true, there are at least 12 manufacturers assigned numbers starting with 02.
There are several different ones defined as private
00-50-79 (hex) PRIVATE
00-A0-54 (hex) PRIVATE
00-A0-85 (hex) PRIVATE
10-00-00 (hex) PRIVATE
11-00-AA (hex) PRIVATE
AC-DE-48 (hex) PRIVATE
Someone should register Arduino as a manufacturer and then everyone should use that one. In the mean time, I would recommend using one of the above PRIVATE prefixes.
I am a network manager and I do utilize the MAC address for keeping track of what kind of computers are on the network so I consider this important on a large network.
Mark (KB2ICI)
According to the ieee oui.txt list (http IEEE SA - Registration Authority) That is not completely true, there are at least 12 manufacturers assigned numbers starting with 02.
Hmm, you're right, but section 3.2.3 of the 802.3 standard clearly states that if the second bit is set it's a locally administered address.
While you can probably get away with using the blocks marked "private", I suspect those are really assigned to someone (or some three letter agency), or reserved for some other reason.
Someone should register Arduino as a manufacturer and then everyone should use that one.
Got a spare US$1600?
I am a network manager and I do utilize the MAC address for keeping track of what kind of computers are on the network so I consider this important on a large network.
Ditto.
-j
Did anyone else laugh out loud for real when they saw the MAC in the sample code?
(I'll save everyone the trouble, it's DE:AD:BE:EF:FE:ED.)