EIGRP – Part 3 (EIGRP Packet Types and Neighbourship)

eigrp-packet-types-ipcisco

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,
– Query,
– Reply,
– Update,
– ACK.

EIGRP Packet Types
 

EIGRP Packet Types
Let’s check these EIGRP packet’s role in EIGRP Operation.

• 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.

EIGRP Configuration with Packet Tracer
 

EIGRP Default Metric
As you can see above, for a neigbourship firstly Router A sends a Hello to the EIGRP Multicast address (224.0.0.10). When Router B receives this Hello, Router B sends its full routing table to the Router A. Beside this, Router B also sends Hello packet to the EIGRP multicast address(224.0.0.10). After receiving Full Routing Table of Router B, Router A send an ACK packet. Router A also send its own Full Routing Table to the Router B. When Router B receives this, it also send ACK packet.

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).

EIGRP Article Series…
EIGRP – Part 1
EIGRP – Part 2 (EIGRP Tables)
EIGRP – Part 3 (EIGRP Packet Types and Neighborship)
EIGRP – Part 4 (Other EIGRP Properties)

EIGRP Configuration with Packet Tracer

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