ubuntu gns3 connect with vbox

Sometimes some experiments of cisco, such as snmp and tftp, need to be combined with the operating system. So, it took me a lot of time to set up this experimental environment.

The system I use is ubuntu, and two necessary components need to be installed:
apt-get install bridge-utils 
apt-get install uml-utilities 
 
brctl addbr br0 build a bridge
ip ls dev br0 up open
ip a  
 
tunctl -t tap0 -u yeelone creates a virtual network card
ip l s dev tap0 up  
ip a  
 
Connect tap0 to eth0
brctl addif br0 tap0   
brctl addif br0 eth0 
 
brctl show br0 
 
ip a a 192.168.1.1/24 dev br0 
ip r a default via 192.168.1.100 
 
dhcpcd br0 

then: