Linux as a software Switch / Router Bridge

Network Interfaces

Creating two network interfaces in Linux

sudo ip link add eth0dummy1 type dummy
sudo ip link add eth0dummy2 type dummy

Setting those interfaces up

sudo ip link set up eth0dummy1
sudo ip link set up eth0dummy2 

Showing existing interfaces

ip addr list

MAC is assigned to eth0dummy1 and eth0dummy2 interfaces

Bridge

Creating the bridge

sudo brctl addbr dummybridge

Setting the bridge up

sudo ip link set up dummybridge 

Adding interfaces to the bridge

sudo brctl addif dummybridge eth0dummy1 eth0dummy2

Showing existing bridges

sudo brctl show

Showing virtual ports and MAC addresses

sudo brctl showmacs dummybridge

virtual port 1 attached to eth0dummy1 interface MAC and port 2 to eth0dummy2 MAC

Router

Converting the bridge to a router by assigning a L3 address.

sudo ip addr add 172.16.0.1/24 dev dummybridge

Reference