There are five types of EIGRP packets:
- Hello: used for the dynamic creation of adjacencies. They are sent to multicast address 224.0.0.10 and do not require ACK. The time interval between sending a hello packet and the immediately following is called the hello interval. For connections with high bandwidth that time is 5 seconds (default), but for slower links (with bandwidth <= T1) amounts to 60 seconds. Furthermore, adiancenza is removed at the end of the so-called hold time (default is 3 times the hello interval), the number of seconds to wait without receiving a hello before the router declares the neighbor unreachable.
To set the hello interval must type:
Router (config-if) # ip hello-interval eigrp
where AS is the number that identifies the Autonomous System.
As regards, however, for the configuration hold time, just write:
Router (config-if) # ip hold-time eigrp
Please note that the hello-and hold-time interval between two neighboring routers can not match. This will not cause the failure of the adjacency formation (as happens in OSPF).
- Update: used to update the information on the routes. They are sent only to routers affected by the route that has undergone change and where discovery is a new route multicasts are forwarded. Require ACK and sequence number.
- Query: This type of packet is sent to neighboring routers if you do not know neither feasible nor successor route to a given destination. Require ACK and sequence number.
- Reply: represent the response to queries. Routed unicast to the router that generated the query itself.
- ACK: they are basically the hello packets sent on unicast (since, in turn, hello not requires ACK).