Thanks for the very informative videos Khaled!

I have a ESXi server running GNS3 servers on Ubuntu and Win 7. I have a 4-port NIC going to four physical switches. Using a cloud to connect a vRouter's interface to the switch, I can get an IP address from the physical switche's DHCP, but I can't ping the swithce's VLAN interface. I can also get a DHCP from the Internet gateway when using the Ubuntu server's own Internet NIC card, but I can't ping the gateway from the virtual router either. Looking at the ARP cache on the physical switch, I can see the router's MAC, but the vRouter can't seem to ARP through the cloud. I've already created tap0 interface and added it to a bridge group on the Ubuntu server, but I had the same problem using that as well. Any ideas on how I need to configure the NICs on GNS3 or ESXi?

This turned out to be an ESXi-related issue. The port group security under the vswitch had to be configured to accept promiscuous mode. I can finally arp through the cloud now.

thanks khalid for your efforts,