EIGRP discovers neighbors using Hello packets, sent to multicast .
Hello intervals depend on link speed:
- High bandwidth (T1 and faster): seconds
- Low bandwidth (below T1): seconds
Hold time is times the Hello interval by default. If no Hello arrives within the hold time, the neighbor is declared down.
For neighbors to form, they must match:
- Autonomous System number
- K-values (metric weights)
- Authentication (if configured)
Unlike OSPF, EIGRP doesn't require matching subnets on point-to-point links. This provides more flexibility in addressing.