EIGRP uses five different packet types, some in pairs. EIGRP packets are sent using either RTP reliable or unreliable delivery and can be sent as a unicast, multicast, or sometimes both. EIGRP packet types are also called EIGRP packet formats or EIGRP messages.

As shown in Figure 1, the five EIGRP packet types include:

Hello packets - Used for neighbor discovery and to maintain neighbor adjacencies.

Update packets - Propagates routing information to EIGRP neighbors.

Acknowledgment packets - Used to acknowledge the receipt of an EIGRP message that was sent using reliable delivery.

Query packets - Used to query routes from neighbors.

Reply packets - Sent in response to an EIGRP query.

Figure 2 shows that EIGRP messages are typically encapsulated in IPv4 or IPv6 packets. EIGRP for IPv4 messages use IPv4 as the network layer protocol. The IPv4 protocol field uses 88 to indicate the data portion of the packet is an EIGRP for IPv4 message. EIGRP for IPv6 messages are encapsulated in IPv6 packets using the next header field of 88. Similar, to the protocol field for IPv4, the IPv6 next header field indicates the type of data carried in the IPv6 packet.