Earning your higher level certifications, practices & hands on are a must.
And practicing with virtual lab is more/really efficient rather than purchasing hardware.
GNS 3 [Graphical Network Simulator] is one of the best virtual lab software.

All you need is just this software and the Cisco IOS Image.
The memory of the virtual Cisco engine is adjustable to it’s maximum.

Some Issues (and tips/tricks) at the first time you worked with…

1. Console not respond immediately after start.
This text should appear first “Connected to Dynamips VM “MPLSCORE” (ID 4, type c3600) - Console port”
This sample for Cisco 3640 IOS Image.
Tips :
- Wait for a while after the Router Started [it needs to boot the IOS]
- If still the console not working, try to check your IOS Image location

2. Error when connecting between Routers with Serial, Ethernet, FastEthernet etc
Tips/Tricks :
- Don’t go to console at the first time after starting the router
- Do right click on your router and configure / add / remove your interfaces
- If that done, try to connect your routers each other as you need.
- if that done, try to start all device.
- Go for console now !.

3. Cannot Save the start-up config & Once you opened a saved *.net on file tab it always goes to default configuration
and the config-register is 0×2142.
Tips/Tricks
-  After all configuration you have considered to be saved done,
stop all device by using “Stop Every Devices”  red button .
- Click file and go to new project.
- Type your *.net file name [example: lab.net] and check on save nvram also export configuration…
- Close GNS 3 and try to open your *.net file.
- Your configuration is now stay as before

a. rahman isnaini r. sutan
thanks to Gracia Wahab