Grab this book when you have the chance. It's 1000 pages, but a much enjoyable read than the OCGs: Cisco Networks: Engineers' Handbook of Routing, Switching, and Security with IOS, NX-OS, and ASA https://www.amazon.com/dp/1484266714/ref=cm_sw_r_apan_glt_fabc_PWZB8V89012A1HP17HKF