EIGRP Packet Types
EIGRP (Enhanced Interior Gateway Routing Protocol) uses EIGRP messages to establish and maintain the EIGRP neighbourship. EIGRP uses five packet types for this messages. These packet types are :
• Hello Packet : Used to establish and maintain the neighbourship. It is a keepalive also.
• Update Packet : Used to send routing updates.
• Query Packet : Used to ask for any routing update, requests an update.
• Reply Packet: Used as a response to the Queries.
• ACK Packet : Used as a feedback to the Update, Query or Reply packets as a feedback mechanism. It is not used for Hello Packets and Ack Packets.
EIGRP Neighbourship Establishment
EIGRP routers establish neighborship between the EIGRP neighbors and the full EIGRP network is build firstly with this estalishments. To establish the EIGRP Neighbourship, Hello Packets are sent between neighbor EIGRP routers periodically. Let’s check an adjacency states step by step.
To establish the EIGRP Neighborship, EIGRP neighbors must have the same K values. But unlike OSPF, the Hello and Hold Down times can be different in both end (Remember! In OSPF they must match for neighbpurship establishment).