I am honest. I want to be a redhat certified system administrator. But not at all that only. I want to networking hat to be on.
I love networking. I want to read RFCs, but I don't want to start by reading RFCs. I want to learn TCP IP protocols. So, that I can learn where and when to use those networking commands for troubleshooting.

fourozan networks
stallings networks
douglas comer internetworking with tcp ip volume 1
stevens tcp ip
fourouzan tcp ip

stallings security
fourozan security
atul kahate security



These are all the textbooks I'm planning to buy.

Anything else you wanna recommend me?

You need a network to learn about networks. Get some shells some place, and setup a network of virtual machines. Connect them all, in various ways. Set up alot of services. Start with common ones like webservers. Reading is fine but doing is better.

Also, I don't see a reason to buy textbooks when all the info you need is online for free.

Setting up a network of Virtual Machines is one way, but although useful may be a bit constrained.

You might look into something more general like GNS3 for practice.

Learn to walk before you run.