What are Hello Packets used for ?

• To discover OSPF neighbours and establish neighbour adjacency.
• Advertise parameters on which two routers must agree to become neighbours.
• Elect DR and BDR on multi access networks

What makes EIGRP unique ?

• Uses Diffused Update algorithm (DUAL) for all route computation
• Uses multicast and unicast for sending packets
• Administrative Distance for Internal router is 90
• Administrative Distance for External router is 170

Routers

Layer 3 Routing

• Single broadcast domain per interface
• Every router is its own broadcast domain
• ACLs can be applied between segments

Issues

• High per-port cost
• Layer 3 processing required
• High latency over layer 2 switching
• Layers 3 processing happens in software