Time to play packets. EIGRP Packets to be precise.
EIGRP when running in a routed environment utilizes five types of packets. A Hello, Update, Query, Reply and Acknowledgement (ACK) packet.
Pretty much used for neighbor discovery. Multicasts with ACK # of 0.
Update packets contain route change information. They are send to affected routers. Updates routers that the particular route has used to converge. Sent as multicasts when a route becomes passive. Syncs by unicasting during startup. Sent reliably.
Performed in route computation when no FS is found. Sent to neighbors asking if they have a route to destination. Usually multicast but can be send as unicast. Sent reliably.
Send in response to a query. Must always reply. Sent reliably.
Acknowledges updates, queries, and replies. Unicast hello’s that contain a non zero ACK number. (Hello’s and ACK don’t require ACK’s)
Above An example Hello Packet. Notice the information provided by a simple packet sniff.
Above Here is an exchange of connected routes via an Update packet.
Above An example of another update packet, this time declaring it cannot reach certain networks.
A thank you to Stretch over at Packetlife for his Captures library. I am currently away from my lab.