- to redistribute external routes into EIGRP
- to prevent routing loops
- to act as a gateway of last resort
- to prevent the router from sending EIGRP packets
Explanation: EIGRP for IPv4 automatically installs a Null0 summary route into the routing table when EIGRP automatic summarization is enabled and there is at least one EIGRP learned subnet. Null0 is a virtual interface that is a route to nowhere and is used to prevent routing loops for destinations that are included in a summary network but do not have a specific entry in the routing table.