OSPF

Open Shortest Path First protocol

What does a router do on a normal day?

• Find path
• Forward packets
• Find an alternate path
• Forward some more packets
• Do this until turned off

Routing vs. Forwarding

Routing - Build maps and give directions
Forwarding - Moving packets between interfaces according to the directions given

IP Routing

• Finding the path
• The path is derived from information received from a routing protocol
• Several alternative paths may exist
  • Best path is stored in the forwarding table
• Decisions are updated periodically or as topology changes -> Event driven
• Decisions are based on:
  • Topology
  • Policies
  • Metrics
    • Hop count
    • Filtering
    • Delay
    • Bandwidth