I finally got GNS3 work for me, I do like this App, and it can simulate Cisco routers perfectly, so if you need play with Cisco Routr Switches or Firewall, I strongly recommend you give it try.
I used Dynagen + Dynamips, this works very well, but it's a bit harder to create new topology and connect to workstations or servers. With the help of GNS3 GUI interfaces, the life is much easier.
The problems I encountered with GNS3 the first two days are:
Flash: drive and saving setting.
1. Cannot copy anything to Flash:
2. Every time tried to save setting, new reload GNS3, all the routers went back to initial setting, which made me crazy. Also, with some IOS, “wr” or “copy run start” will cause APP no response.
1. “erase flash:” will fix this issue, I had this one in CLI mode
2. Take off “concfg= xxxx”, I believe this caused issue, but not so sure why.
Modify Topology file.
1. Save as Topology after changes
DO NOT Save Topology When exit GNS3 !
Someone suggested the solution for this:
Preferences → Dynamips → Clear 'automatically clean the working directory’
Will fix this issue, but I tried it, sometimes will kill my contents in Nvram:, couldn't be bothered, just make sure EXIT WITHOUT SAVEING ANYTHING.