I've been trying to configure my linux vm firewall using iptables.....I have only one computer with me and i desire to test those....I've been using (GNS3 + vmware) to simulate the desired network...but it becomes too unstable at times(...like while managing 4 linux vm's + GNS3)..........

Could anyone suggest me a good simulator in which i can run networked linux PC's????(OTHER THAN GNS3)

THANKS
SRT