Packet types

Useful commands
router# debug eigrp packets

Multicast addresses

IPv4: 224.0.0.10
IPv6: ff02::a

Key Takeaways

For the purposes of the exam, the following packet types are the most important to remember:

HELLO & ACK

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

UPDATE packets are sent out as multicast. They inform other routers of updates to the network.

QUERY

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

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

REQUEST packets are sent when the router is requesting more information on a route that is already known to the router.

List
EIGRP Hello packet default times
EIGRP Packet types

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