Ethernet network question

I was just wondering who assignes your ip address range.
I know how the ethernet network works as far as classes, traffic etc. I have read many posts and articles but my question is who does the assignment?
When building a plant network where do you get your ip range from, do you just pick one, or does someone have to assign the range you use.
Thanks, this has just been bugging me for a while, hope I didnt waste your time.

If you do have plant IT people they need to be involved even if there is no current plans to hook up any high level monitoring.

You need to use a Private IP section of addresses. It has been suggested not to use the low level (192.168.xxx.yyy) with the xxx at 0 or 1. These are commonly used in home routers and could be a pain if you decide to use home VPN access. Either use a higher starting number in the xxx area (say 100) which still leaves a lot of addresses (almost 40,000) or use a whole other range (172.16.0.0 - 172.31.255.255).

Make sure each piece of equipment has a fixed IP. After setting disable and DHCP or BOOTP. Make a lable with the IP, Netmask, and Gateway information and stick it to each piece of equipment. Leave room in you plan for additions.

The Wikipedia article on 'Pivate Networks' may help.

I do not have a plant but for our testing/demo lab I got a block of 100 IP address from IT for us to assign as needed.
They are on a subnet so segregated from everyone else and we need to manage them to prevent duplicates.
I also went into the router cabinet and added my own switch to further isolate it and limit it to specific pre-wired Ethernet wall connection points in the lab area.

We also hit up our IT guys for a blocks of IP addresses to use. When we use those up, we grab 10 or 20 more. We don't use the designated private IP address (192.xxx, 172.xxx, 10.xxx) because we actually own our own IP address block. =)

Appreciate eveyone's responce. I do understand the structure of the ethernet network. I just did not have a clue of where it all starts as far as assigning the addresses from the start.
Thanks to everyone.