You need gear to practice, and a simulator is free. Set up Packet Tracer or GNS3, then learn the IOS command modes every later lesson assumes.
Why: you cannot learn routing and switching by reading — you need devices to configure, and a simulator gives you a whole network on your laptop for free. When: Packet Tracer is the easiest start (Cisco NetAcad); GNS3 and EVE-NG run real device images for higher fidelity. Where: everything in this course runs in any of them.
SIMULATOR BEST FOR NOTES
Packet Tracer beginners, CCNA labs free, easiest, Cisco
GNS3 real IOS images, realistic labs free, more setup
EVE-NG multi-vendor, large topologies free + paid tiers
Build this simple lab to follow along:
PC1 -- SW1 -- R1 -- R2 -- SW2 -- PC2Why: IOS is modal — you move from user mode to privileged (enable) mode to global configuration mode, and commands only work in the right mode — so knowing where you are is half of configuring a device. When: enable to get privileges, configure terminal to make changes, interface to configure a port. Where: the prompt tells you the mode; watch it change.
Router> enable ! user EXEC -> privileged EXEC
Router# configure terminal ! -> global configuration
Router(config)# hostname R1 ! rename the device
R1(config)# interface Gig0/0 ! -> interface configuration
R1(config-if)# exit
R1(config)# end ! jump back to privileged EXEC
R1#Why: the config you type lives in running-config (RAM) and is LOST on reboot unless you copy it to startup-config (NVRAM) — forgetting to save is the classic way to lose an evening’s work. When: save after every meaningful change. Where: show running-config displays the live config; write memory persists it.
R1(config)# interface Gig0/0
R1(config-if)# ip address 10.0.0.1 255.255.255.0
R1(config-if)# no shutdown ! bring the interface UP
R1(config-if)# end
R1# show ip interface brief ! quick status of every interface
R1# show running-config ! the live config (in RAM)
R1# write memory ! SAVE to startup-config (NVRAM)