EIGRP Packet Types: The Complete Guide in 2022

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Introduction to EIGRP

As we know, EIGRP i.e. Enhanced Interior Gateway Routing Protocol is a routing protocol that specify how routers or data switches communicate with each other. It is referred to as a Transport Layer Protocol as it runs on top of the IP. Unlike application layer protocols (Telnet, BGP etc.), EIGRP has its own reliability mechanism.

EIGRP uses 5 packet types in communication with its neighbours. The routing information carried by the packets  is sent reliably by means of a sequence number. The sequence number is assigned to each reliable packet (i.e. Update, Query, and Reply) and a clear-cut acknowledgment is required for that sequence number.

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EIGRP uses Reliable Transport Protocol (RTP) to exchange packets between the neighbors in a reliable and ordered manner.

In this article, we will discuss the packet types of EIGRP.

 

EIGRP Packet Types

The EIGRP packet types are discussed in detail below –

Hello Packet

EIGRP uses hello packets in the discovery of neighbors. They are multicast to 224.0.0.10. By default, EIGRP sends hello packets every 5 seconds (60 seconds on WAN links with 1.544 Mbps speeds or less). Important features of Hello Packet are:

  • Opcode 5
  • Neighbor discovery
  • It is always multicast.
  • The periodical timer is 5 seconds. Hold down timer is 15 seconds.

Acknowledgment (ACK) Packet

An acknowledgment packet acknowledges the reception of an update packet. It is a hello packet with no data. EIGRP sends acknowledgment packets to the unicast address of the sender of the update packet. Important features of ACK Packet are:

  • Opcode 5
  • Used to acknowledge the receipt of EIGRP packets (UpdateQuery and Reply)
  • It is always a Unicast

Update Packet

Update packets contain routing information for destinations. EIGRP unicasts update packets to newly discovered neighbors; otherwise, it multicasts update packets to 224.0.0.10 when a link or metric changes. Update packets are acknowledged to ensure reliable transmission. Important features of Update Packet are:

  • Opcode 1
  • Used to convey/propagate EIGRP routing updates
  • Can be Unicast or Multicast
  • Sequence Number & Acknowledgement Number
  • Uses RTP

Query Packet

EIGRP sends query packets to find feasible successors to a destination. Query packets are always multicast. Important features of Query Packet are:

  • Opcode 3
  • Used to get specific information from neighbour router
  • Can be Unicast or Multicast
  • Uses RTP
  • Sequence & Acknowledge numbers

Reply Packet

EIGRP sends reply packets to respond to query packets. Reply packets provide a feasible successor to the sender of the query. Reply packets are unicast to the sender of the query packet. Important features of Reply Packet are:

  • Opcode 4
  • Used to respond to a query
  • It is always a Unicast
  • Use RTP

Comparison Table: EIGRP Packet Types

Below table summarizes the important points of differentiation between the 5 types of packets:

Download the Comparison table: EIGRP Packet types

Continue Reading:

Configuring EIGRP Stub

EIGRP vs OSPF : Know the difference

 

Are You Preparing for Interview:

If preparing for your next interview, please go through the list of  Top 100 EIGRP Interview questions.

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