This section describes the different types of messages using by EIGRP. However, before delving into the specifics of the different message types, it is important to have a solid understanding of the EIGRP packet header, wherein these messages are contained.
EIGRP Packet Header
Although going into specifics on the EIGRP packet formats is beyond the scope of the ROUTE exam, a fundamental understanding of the EIGRP packet header is important in order to completely understand the overall operation of the EIGRP routing protocol. Figure 2-1 shows the format of the EIGRP packet header: