SDN: one controller programs every switch

The idea

Software-defined networking (SDN) takes the deciding out of the switches: one SDN controller computes every path and writes it into them, and they only forward. Here it programs s1, s2 and s3, cabled in a triangle, so that alice, bob and webServer can talk; then it is cut off, a cable fails, and a policy goes in.

Steps

1. A switch that decides nothing

   alice and webServer share a network. A classic switch learns where each MAC address is by itself; these do only what their flow table says. Read s1's.

   alice:~# ping -c 2 -W 1 10.0.1.15
   s1:~# ovs-ofctl -O OpenFlow13 dump-flows br0
   s1:~# ovs-vsctl show

2. The controller programs the flows

   Deciding where traffic goes is the control plane, and one controller holds it. It asks each switch, over a management network, which ports are up. Read what it sees, then let it program.

   controller:~# sdn-controller status
   controller:~# sdn-controller apply
   alice:~# ping -c 2 -W 1 10.0.1.15