I don't have the cycles right now to write up and post a class in IP networking, particularly given what I have linked to (posted) is clearly inadequate for your understanding; that I've "missed" with what I've provided.
Please read the IP routing and DNS links that I've posted. End to end. If you have questions on those, please ask. (That'll help you get some background, and it'll help me improve those articles.)
I don't know where that 172.16.0.0/12 address is coming from here. I know some ISPs use weird IP address blocks (AT&T UVerse was using a 10.0.0.0/8 address space), but that 172.16.0.0/12 assignment is not one I've seen. I'll guess that's something you've thought you needed to assign? The external IP address is provided by your ISP. That IP address is not assigned by you. (You might have to enter it into the device, but it's an address value that you have acquired from the ISP directly from support, via an IP networking set-up FAQ for your ISP, or via the ISP's DHCP server.)
What you are calling "workgroup" is the subnet mask. What's usually called a "Workgroup" is something completely different.
You have 255.255.255.0 listed as your subnet mask; that's what is (also) known as a /24 network, using the newer IP routing notation. That means you have IP addresses .1 through .254 available to you, without either using an IP router, or without moving to a larger subnet.
Your DNS server address is the IP address of your DNS server. If 10.1.1.1 is running your DNS, then 10.1.1.1 is your DNS server address. (The sole exception here is the DNS server reference present on the DNS server network interface on the DNS server itself; that's 127.0.0.1; the IP itself; the IP localhost; the IP address of "me".)
If you don't have a secondary DNS server, then there is no secondary DNS server listed.
If your IP router is at address 10.1.1.2, then the IP router address is 10.1.1.2 and not that 10.1.1.254.
You'll need to enter the router and DNS server addresses in static-configured hosts, and you'll need to configure the router and DNS server addresses into your DHCP server for the hosts that get their addresses from DHCP.
And FWIW and without intending any insult, you can and probably should either do some reading on or watch some videos on, or attend some classes on IP networking, or you can offload this stuff and acquire more formal help. When these networking configurations go wrong - and they do, I just ended up troubleshooting an error on one of my own networks after a power restoration this morning - you'll either get to troubleshoot the networking error yourself, or you'll want to call in help. Having some background will help you troubleshoot this stuff, if that's your choice here.