Requirements

• Maintain a view of the topology;
• Broadcast HELLO packets to maintain a list of neighbours;
• On change, flood the view of the network;
• Run Djikstra to compute the shortest path.

1) Define a topology

• 2 switches
• 2 hosts
• 2 controllers (same as hosts)

2) Send basic traffic

• Send traffic by hand, without PWOSPF;
• Need to install forwarding rule in dataplane (through mininet);
• ping H1 to H2.

3) Controller

• Controller program to install rules;
• Controllers are threads in mininet;
• 1 controller per switch;
• To statically install a forwarding rule, use switch.addRule.

4) Compute rules instead of hard code them

• Data structure for topology (matrix, …)
• Compute nearest neighbours;
• Stub out parsing, sending, receiving of PWOSPF;
• Run Djikstra on topology;
• Install rules.

5) Send packets (HELLO) ==> Who are our neighbours?

• Define packet format with Scapy;
• To send, use sendp();
• To receive, sniff on interface (provided by mininet);
• Data plane code to handle broadcast or Controller sends 1 packet per interface;
  • Step 1: control plane sends to everyone;
  • Step 2: broadcast in the data plane.
• Parse packet and populate topology.

6) Timeouts

• Generate HELLOs at Timeouts;
• Handle Timeouts ==> link down.

7) LSU packets

• Build the graph, running Djikstra;
• Flood to everyone;
• Drop if it is your own;
• Parse responses;
• Build topology.