EIGRP – Various Packet Types

 EIGRP, Networking  Comments Off on EIGRP – Various Packet Types
Dec 132022
 

In this third post in our EIGRP series, let’s consider the various packet types used and their purpose.

Altogether, we encounter five packet types in EIGRP that are used to establish adjacencies and share routing information.

The packet types include: Hello, Acknowledgment, Update, Query and Reply.

Some of the EIGRP packet types are reliable and require an acknowledgment while others are unreliable and do not need an acknowledgment.

The OPCode field in the EIGRP packet header identifies the packet type:

OPCode 1: Update packet
OPCode 3: Query packet
OPCode 4: Reply packet
OPCode 5: Hello and ACK packets

EIGRP Hello Packet

EIGRP Packet Types:

It’s time to consider each of the EIGRP packet types and their purpose.

* Hello:
# Discover and form adacencies with Neighbors (Other EIGRP routers in the NW)
# Hello packets are sent unreliably and do NOT require acknowledgements
# Continued receipt of Hellos maintains Neighbor Table
# Hello packets are sent via multicast

* Acknowledgment:
# Acknowledgements packets are “dataless” Hello packets with just a sequence number
# They indicate receipt of any EIGRP packet during a “reliable” (Reliable Transport Protocol) exchange
# Will acknowledge receipt of Update, Query and Reply packets

* Update:
# Transmit Routability and Reachability information with other EIGRP Neighbors
# Carry prefix and metric information
# Sent to initially exchange topology information or topology change
# Later Updates sent ONLY when necessary, such as when a new destination prefix becomes reachable or the cost of an already reachable destination prefix changes
# So updates are non-periodic, i.e., not sent at scheduled intervals
# EIGRP updates contain only needed routing information and are unicast to routers that require it
# Update packets can also be multicast (like when a link cost changes)
# Sent reliably and require acknowledgments

* Query:
# Query packets are sent when destinations go into Active state
# Used to get specific information from one or more Neighbors; Sent to search for another path during convergence
# Query packets are multicast to all peers on all interfaces except for the interface to the previous Successor
# Sent reliably and require acknowledgements

* Reply:
# Reply packets are unicast to the originator of the query
# Sent reliably and require acknowledgements

Reliable Packets:

Reliable packets require explicit acknowledgement from destination.

They are sequenced and retransmitted up to 16 times if not acknowledged.
Reliable packets are:
• Updates
• Queries
• Replies
• SIA-Queries
• SIA-Replies

Unreliable packets do not require acknowledgement from destination:
# Hello and ACK

How to Verify EIGRP Packets

A few days back, we did a basic EIGRP configuration.

As part of that basic EIGRP lab, we ran a bunch of commands including one that let us view the various EIGRP packets on a Router.

EIGRP Configuration on Packet Tracer

Take a look below at various EIGRP Packets on the three Routers R1, R2 and R3:

R1#sh ip eigrp traffic
IP-EIGRP Traffic Statistics for process 1
Hellos sent/received: 1211/1170
Updates sent/received: 8/6
Queries sent/received: 0/0
Replies sent/received: 0/0
Acks sent/received: 5/8
Input queue high water mark 1, 0 drops
SIA-Queries sent/received: 0/0
SIA-Replies sent/received: 0/0
R2#sh ip eigrp traffic
IP-EIGRP Traffic Statistics for process 1
Hellos sent/received: 1167/1162
Updates sent/received: 6/10
Queries sent/received: 0/0
Replies sent/received: 0/0
Acks sent/received: 10/6
Input queue high water mark 1, 0 drops
SIA-Queries sent/received: 0/0
SIA-Replies sent/received: 0/0
R3#sh ip eigrp traffic
IP-EIGRP Traffic Statistics for process 1
Hellos sent/received: 1140/1137
Updates sent/received: 7/5
Queries sent/received: 0/0
Replies sent/received: 0/0
Acks sent/received: 5/6
Input queue high water mark 1, 0 drops
SIA-Queries sent/received: 0/0
SIA-Replies sent/received: 0/0

EIGRP Routing Protocol – Primer

 EIGRP  Comments Off on EIGRP Routing Protocol – Primer
Dec 132022
 
EIGRP Routing Protocol – Primer

In our last post, we took a look at a basic EIGRP configuration. Now we’ll take a step back and consider some of the essential features of EIGRP. EIGRP is a Cisco-proprietary dynamic routing protocol that debuted in 1992. Although Cisco attempted to make it an open standard protocol a Read More

How to Configure Basic EIGRP

 EIGRP  Comments Off on How to Configure Basic EIGRP
Dec 012022
 
How to Configure Basic EIGRP

In this lab, we’ll do a basic configuration of EIGRP and then run a bunch of verify commands. We’ll finish off with a ping test to verify end-to-end connectivity between the PCs. This time the lab is being done on Packet Tracer instead of GNS3. Packet Tracer is easier to Read More

Secure File Deletion on Ubuntu

 Linux, Security  Comments Off on Secure File Deletion on Ubuntu
Nov 072022
 

In an age of rampant security attacks, safeguarding data is paramount. After all, data is the new Kohinoor for organizations of all sizes in the modern era. secure-delete is one of the command line tools available for Ubuntu and its derivatives like Linux Mint to securely erase data. Secure file and Read More

How to Configure EIGRP Named Mode Authentication

 EIGRP, Networking, Security  Comments Off on How to Configure EIGRP Named Mode Authentication
Sep 282022
 
How to Configure EIGRP Named Mode Authentication

In this lab, we’ll configure authentication when running EIGRP in named mode. While classic mode EIGRP offers only MD5 authentication, named mode EIGRP offers both MD5 and HMAC-SHA-256 authentication. HMAC-SHA-256 authentication is, of course, the more secure version. By the way, we can configure authentication between two routers with one Read More

How to Configure DMVPN

 Networking, Security  Comments Off on How to Configure DMVPN
Sep 232022
 
How to Configure DMVPN

Dynamic Multipoint Virtual Private Network (DMVPN) owes its popularity to two primary reasons: scalability and simplicity of configuration. In large organizations with lots of branches, configuring dozens of point-to-point VPN tunnels is an error-prone and cumbersome exercise. So Cisco introduced the DMVPN technology nearly two decades ago. DMVPN finds favor Read More

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