GNS3 server is running on a VM (ESXi host). Second interface eth1 connects from the VM to the default vSwitch0.  The interface tap0 is a loopback interface on the GNS3 server, which I used to connect into my GNS3 topology. Interface br0 bridges the tap0 interface to interface eth1.

gns3@gns3vm:~$ cat /etc/
#Set TAP0
#Configure TAP1
ifconfig tap0 up

root@gns3vm:/home/gns3# cat /etc/rc.local | grep sudo
sudo sh /etc/


root@gns3vm:/home/gns3# sudo cat /etc/network/interfaces

# Bridge between tap0 and eth1

auto br0
iface br0 inet manual
bridge_ports tap0 eth1
bridge_stp off