How relevant is Linux to networking?

I'm in the process of getting my ccent accreditation and hopefully a ccna not long after. I've played around a little with Linux and I've noticed some similarities between the Linux code and Cisco's networking code but it's not exact. Being entry level I don't know enough about either yet to say with certainty if there is a dual application or connection. Hoping someone here more experienced and skilled than myself might be able to shed some light on this.