EIGRP Packet Tracer Lab Part 2

EIGRP LAB Part 2 – Overview

In the second part of this Packet Tracer EIGRP lab, I build off of the network created in the first 3 video tutorials. In video tutorial part 4: I expand the EIGRP network by adding an ISP router with a default route out of the network. I distribute that route with the “redistribute static” command and observe the learned EIGRP external route in the routing table.

In video tutorial part 5: I add another router to the EIGRP network to create a scenario to show EIGRP’s default summarizing behavior and the problems it can cause by creating summary routes to null0 interfaces bypassing the router’s IP classless behavior.

In video tutorial part 6: Using Packet Tracer’s simulation mode I test the network using PING to demonstrate EIGRP’s auto-summarizing behavior and the problems it causes by dropping packets to a summary route null0 interface instead of continuing to search the routing table for a default route. The problem is fixed with the no auto-summary command.

In video tutorial part 7: I change the bandwidth on two serial interfaces to demonstrate EIGRP’s ability to prioritize routes based on a route’s bandwidth. This allows me to demonstrate how EIGRP and DUAL can calculate successor and feasible successor routes when multiple routes are available. This time the “no auto-summary” command is used on all routers in the network in order to fix entries in the topology table.


You can download the Packet Tracer file to follow along with this second series of EIGRP video tutorials: basicEIGRPstep2.zip Note: You will need to have the Packet Tracer program installed on your computer for the downloadable file to work. Packet Tracer is free to all students enrolled in a Cisco Academy course. Feel free to contact me if you would like to enroll in a Cisco Academy CCNA course.

Video Tutorials

EIGRP Packet Tracer Lab

EIGRP Lab – Overview

In the series of video tutorials below, I walk through the process of configuring a network to work with the EIGRP routing protocol. In the first video, I subnet the network into six subnets of various sizes; in the second video, I wire the network and configure the router’s network interfaces with IP addresses; in the third video, EIGRP is configured on all of the routers and the learned EIGRP routes are verified in the routing tables.


Download the Packet Tracer file to follow along with the EIGRP video tutorials below: basic-EIGRP-beginning.zip Note: You will need to have the Packet Tracer program installed on your computer for the downloadable file to work. Packet Tracer is free to all students enrolled in a Cisco Academy course. Feel free to contact me if you would like to enroll in a Cisco Academy CCNA course.

Video Tutorials


EIGRP Overview

Enhanced Interior Gateway Routing Protocol or EIGRP is Cisco’s proprietary Distance Vector routing protocol that replaced the earlier IGRP routing protocol. EIGRP introduced significant improvements to the IGRP routing protocol including support for VLSM and CIDR, guaranteed “loop free” routes, and faster convergence times.

Protocol Administrative
connected route 0
static route 1
EIGRP summary 5
EIGRP internal 90
IGRP 100
OSPF 110
RIP 120
EIGRP external

Routing Enhancements

  • VLSM & CIDR – EIGRP has support for variable length subnet masks (VLSM) and classless inter domain routing (CIDR).
  • DUAL algorithm – The diffusing update algorithm or DUAL, provides guaranteed and optimized loop free routes.
  • Successor & Feasible Successor routes – The successor route is the best route to a destination network. If available, DUAL and the EIGRP topology database will also calculate a guaranteed loop free backup route called the Feasible Successor route.
  • Partial & Bounded Updates – for faster convergence times. No periodic updates like RIP. EIGRP only sends information when there is a change in the network, like a network link going down. EIGRP does not send the entire routing table, just the information that has changed and only to those routers that need the new information.
  • Routing Metrics – EIGRP uses a 32 bit routing metric that is backwards compatible with IGRP’s 24 bit metric. EIGRP’s routing metric is not based on hop count like RIP, it is based instead on: Bandwidth, Load, Delay and Reliability, with Bandwidth and then Delay being the most important factors. EIGRP also features MTU and Hop Count as metric vectors, though they are not used in route calculations.
  • RTP reliable transport protocol – EIGRP uses its own layer 3, layer 4 protocol to exchange routing updates, and information
  • PDMs protocol dependent modules – can be added to EIGRP so that it can route other routed protocols like Apple Talk and IPX/SPX
  • Unequal Cost Load Balancing – EIGRP is capable of being configured for unequal cost load balancing

    EIGRP Routing Tables

  • Routing Table – the best “loop free” network routes are placed in the routing table
  • Neighbor Table – neighbor adjacencies are maintained in this table
  • Topology Table – maintains “loop free” backup routes known as successor routes and feasible successor routes

IOS CLI Commands

The command to start the EIGRP routing process is router eigrp followed by the autonomous system number. The autonomous system number or (AS#) functions more as a process ID number. The AS number needs to be the same on all neighbor EIGRP routers.

router(config)# router eigrp <AS/ID-number>

  EXAMPLE: router(config)# router eigrp 1

The command to add a network and interface to the EIGRP routing process is: network <network number> <wildcard mask>. The network number is the network ip address and the wildcard bits is the inverse of the subnet mask in decimal, so a /24 subnet mask or in wildcard bits is and a /16 or would be

 router(config-router)# network <network-number> <wildcard-mask>

  EXAMPLE: router(config-router)# network
router(config-router)# network

If the EIGRP router is a boundary router it will auto-summarize routes by default. A boundary router is a router with multiple interfaces having different classful network ranges and/or different subnet mask lengths. This can cause problems by working against EIGRPs ability to handle VLSM, CIDR, and general routing to non-contiguous networks. The command to turn off auto summarization is no auto-summary.

 router(config-router)# no auto-summary

The redistribute static command will propagate all static routes including the default route to all other EIGRP routers in the network.

 router(config-router)# redistribute static

The passive-interface command can be used to stop EIGRP packets from being sent out of a network interface where there are no other EIGRP routers present.

 router(config-router)#passive-interface <interface>

 EXAMPLE: router(config-router)#passive-interface fastEthernet 0/0

The no auto-summary command is very useful to taking advantage of EIGRP’s ability to route to variable length and discontiguous subnets, however you may want to still use summary addresses in order to optimize your router’s routing tables. In this situation you can manually configure and advertise an EIGRP summary address with the ip summary-address command configured on a network interface.

 router(config)# interface <int-type> <int-num>
router(config-if)# ip summary-address eigrp <as-number> <ip-summary-address> <subnet-mask> <administrative-distance>

  EXAMPLE: router(config)# interface s0/0/0
router(config-if)# ip summary-address eigrp 1

The following commands will exit from router configuration mode

 router(config-router)# exit
 router(config-router)# end

The following show commands are useful in verifying and troubleshooting EIGRP operation and configuration, as well as identifying the successor and feasible successor routes

 router# show ip eigrp neighbor
router# show ip eigrp topology
router# show running-config
router# show ip protocols
router# show ip route

Video Tutorials

Routing Loops


Routing Loops are a risk in networks that utilize an older dynamic routing protocol like RIP. A routing loop is a scenario where data, instead of being routed to its correct destination, is sent from router to router endlessly. This scenario can be caused by routers not receiving updated routing information quickly enough, and as a result, forwarding packets incorrectly and propagating routing information to neighbor routers incorrectly. When every router in the system has the correct routing information the network is said to be converged. Therefore, it is desirable to use a routing protocol that can converge a network quickly and prevent routing loops.

Typically distance vector routing protocols like RIPv1, RIPv2 and IGRP, do not converge networks as quickly as link state routing protocols like OSPF and ISIS, with the EIGRP routing protocol being the exception.

Count-to-inifinity is a RIP routing loop scenario whereby the routes in the routing tables keep increasing their hop-count metric. This is caused by incorrect routing information being propagated on the network.

Distance Vector routing protocols have been designed and improved over the years to minimize the possibility of routing loops. RIP uses the following methods and rules to avoid routing loops and count-to-infinity: split horizon, hold down timers, route poisoning, poison reverse, and TTL values.     

Video Tutorial

Dynamic Routing Protocols


With complex networks, hierarchically designed networks, networks with redundancy, or networks requiring more than two routers it is often beneficial to use a dynamic routing protocol instead of using only static routes.

Dynamic Routing Protocols

Distance Vector versus Link State


Various routing protocols and their characteristics

Static and Default Routes


It is important to know how to configure static routes on a router. Many networks are small enough that all of the routing can be handled by a few static routes and a default route out of the network. If you want to know a router’s routes you need to look at its routing table. The routing table will show you connected routes, static routes, if there is a default route, and it will also show you if there are any dynamically learned routes too. In this section we will look at connected routes, static routes and default routes.

Connected Routes

Connected routes are routes to networks directly connected to the router. To establish connected routes all you have to do is bring up your router’s interfaces. This means configuring the router’s interfaces with IP addresses and subnet masks and making sure they are not in an administratively shutdown state.

To configure a Fast Ethernet interface from global configuration mode:

R1(config)#interface fastethernet 0/0
R1(config-if)#ip address <your ip address> <your subnet mask>
R1(config-if)#description <your description>
R1(config-if)#no shutdown

To configure a serial interface from global configuration mode. You can first check to see if your interface is the DCE and will need a clock rate:

R1#show controllers serial 0/0

Checking the “show controllers” command results to see If the interface is the DCE, you can see from the output below, that the interface is in fact the DCE, and that the clock rate needs to be set.


R1(config)#interface serial 0/0
R1(config-if)#ip address <your ip address> <your subnet mask>
R1(config-if)#clock rate 64000 (only if the interface is the DCE)
R1(config-if)#description <your description>
R1(config-if)#no shutdown

Now that the interfaces have been brought up you can see the connected routes by looking at the routing table by issuing a “show ip route” command and looking for the lines that start with “c”:

Static Routes

In the picture below, R1 has three connected networks in its routing table but it does not know about the network and therefore cannot route traffic to it. To solve that problem a static route to the network can be configured.

There are two ways of configuring a static route. The first uses the next hop router’s IP address on the connected network:
     R1(config)#ip route <destination network> <subnet mask> <next hop router address>

The second uses the router’s own exit interface. This way is faster for the router because it doesn’t have to first look up the exit interface from the connected network:

R1(config)#ip route <destination network> <subnet mask> <local router exit interface> 

both types of static route commands are listed below:


After the static route has been configured you should be able to verify the static route in the router’s routing table be issuing a #show ip route command and looking for the “s” entry in the routing table. The image below shows the router’s routing table after a static route was configured and the “show ip route” command was executed. Notice the highlighted static route which starts with an “s” in the routing table:
     R1(config)#ip route fa1/0
R1#show ip route

Default Routes

In the diagram below R1 needs a default route or gateway of last resort configured so that it can route traffic to unknown networks across the internet. If R1 does not have a default route, traffic to all unknown networks will be dropped, and surfing the Web will not be possible. To configure a default route you must configure a static route to the network and subnet mask to the next hop router or exit interface which has a path out of the network (see below). The commands to create a default route or gateway of last resort are:

R1(config)#ip route <next hop router IP address>
R1(config)#ip route <exit interface>

Once you have configured a default route it will show up in the routing table as an “s” with an asterisk “*” next to it signifying it as a default route. You can also see from the highlighted areas in the routing table output below that the default route is also acknowledged as the “Gateway of last resort is to network” (see below):

Video Tutorial on Default Routes

In this video I demonstrate configuring a default route using Packet Tracer

Welcome to Cisco CCNA 2

CCNA 2 Introduction

The Cisco CCNA certification is the most well known computer networking certification in the industry. I recommend a Cisco course of study and the Cisco Academy Curriculum in particular to anyone who wants to learn about computer networking. It is the best foundation to teach how networks communicate, the protocols that are involved, the network addressing, subnetting, routing, switching, VLANs and more!

As a Cisco Networking Academy instructor I have taught the Cisco CCNA curriculum for over 12 years. The Cisco Academy offers 4 classes that together map to the Cisco CCNA certification exam. The current exam is the 200-120 CCNA, which has a stronger emphasis on IPv6. All students that are enrolled through the college will qualify to be enrolled in the Cisco Academy, and all Cisco Academy students will have access to online curriculum materials as well as the latest version of Packet Tracer (6.1), a great tool for creating simulated networked environments, complete with functioning routers, switches, and hosts.

In fall 2013, the Cisco Academy released an updated version of their CCNA curriculum. This updated curriculum coincides with the new 200-120 CCNA exam and includes many new area of study including a much stronger empahasis on IPv6.

Course Materials

All of the course materials are available through the Cisco Academy website through their learning management system. This includes the complete text, the Packet Tracer software program, interactive activities, multiple choice exams, and plenty of labs with complete instructions. If you prefer a paper copy of the text you can purchase one online from Cisco Press or Amazon. Make sure you order a current version of the text. I have provided a link to the text at Cisco Press and the ISBN number:

Routing and Switching Essentials Companion Guide
: ISBN: 1587132060 / ISBN 13: 9781587132063

Class Availability

  • How can I enroll in a class?
    I teach the Cisco CCNA through Central Oregon Community College. To sign up for the class and attend remotely online, look for new student registration at http://www.cocc.edu
  • Where can I do my labs?.
    Some labs will be done in class, some labs will be done at home using Packet Tracer, and some labs can be done by remotely by connecting to the CIS Department Netlab+ server.
  • What if I am an online student, and I can’t come to the lab?
    If you are an online student, I recommend that you login to Blackboard and attend the class online through the Blackboard video conferencing tool. The is always available through video conference and it will also be recorded and available for watching later.
  • How will I turn in assignments?
    Exams will be taken online through the Cisco Academy website and learning management system. Labs will be turned into me directly.
  • What are the assignments and how will I be graded?
    I grade on a point system. Every week you will have the opportunity to
    earn points from chapter exams and chapter labs. At the end of the class there is a cumulative multiple choice final exam and a cumulative lab final.