As simple as the concepts are

Understanding IP subnetting is a fundamental requirement for almost any techie - whether you’re a coder, a database administrator or the CTO. However, as simple as the concepts are, there is a general difficulty in understanding the topic.

https://www.techopedia.com/6/28587/internet/8-steps-to-understanding-ip-subnetting

Please explain to me the meaning and grammatical form "as...as" in the context? Is it a phrase or a clause?

Thanks