router# debug eigrp packets
For the purposes of the exam, the following packet types are the most important to remember:
the HELLO is the most important packet. it is used to discover other routers and for other routers to discover the local router. Hellos are sent out every 5 seconds by default.
ACK packets are sent in response to Hello packets. Technically the ACK is a Hello packet, but the data has been removed and the sequence number increased. Hello packets are sent as multicast, the ACKs are sent back as unicast packets.
UPDATE packets are sent out as multicast. They inform other routers of updates to the network.
QUERY packets are used when a route is lost. If queries are present on the network then this is normally indicative of a problem where one of the routers has lost it’s connection to a network.
REPLY packets are sent as a response to a QUERY packet. The REPLY packet contains information of the network in response to the QUERY.
REQUEST packets are sent when the router is requesting more information on a route that is already known to the router.
EIGRP Hello packet default times
EIGRP Packet types