Free Play Labs – CCNA Vol 1, Chapter 21

 In 200-301 V1 Ch21: OSPF Network Types, 200-301 V1 Part 6: OSPF, Free Play Labs for CCNA

OSPF requires two routers to become neighbors before they can exchange OSPF LSAs and then calculate new routes. Chapter 21 of the CCNA 200-301 Volume 1 focuses on neighbor relationships. The chapter examines why some links require a Designated Router (DR) and Backup Designated Router (BDR), and while others do not. The chapter then goes on to work through the range of settings that might prevent routers from becoming neighbors.

As with all the posts in this series, this post helps you re-create some of the examples from that chapter using Cisco Packet Tracer.

Confused? New to “Free Play” Labs?

The idea is simple: Many students would like to further explore the Examples in the Official Cert Guide. We remove the barriers so you can do just that with the free Cisco Packet Tracer simulator.

The details require some reading. To get your head around what kind of content is here in the blog for these labs, read:

Book: CCNA 200-301 OCG, Volume 1
Chapter: 21
Title: OSPF Network Types and Neighbors
Part: 6

What’s in This Post

Chapter Intro: A brief description of the topics in that chapter of the book.

Download Link: Links to a ZIP; the ZIP holds all the .PKT files for this chapter.

Table of PKT files, by Example: A table that lists each example in the chapter, with the files supplied for each. Also lists a note about whether the PKT topology matches the book example exactly or not.

Tips: When we build the files, we come across items that we think might confuse you when trying the examples with PT. We write those notes in this section!

Chapter Intro

OSPF includes a large number of interlocking pieces with a large number of configuration settings. One great way to separate the parts of OSPF to help think through what OSPF is doing, and to troubleshoot problems, is to ask a simple question: Do routers that should become OSPF neighbors become neighbors? If not, you have set of issues to consider, but if the routers become neighbors, you have another set of concerns.

Chapter 21 of the CCNA 200-301 Official Cert Guide, Vol 1 focuses on features of OSPF neighbors. The first half of the Chapter examines what happens with working OSPF neighbors depending on the OSPF network type. One type – broadcast – requires the routers to elect a Designated Router (DR) and Backup Designated Router (BDR), but other types like point-to-point do not. The first half of the chapter examines those settings, the DR/BDR election, and how to change the OSPF network type.

The second half of the chapter examines the issues that can prevent two routers from becoming OSPF neighbors. Many misconfigured settings can prevent two routers from becoming neighbors, and you should know those settings and what happens when you misconfigure those settings.

Download the Packet Tracer ZIP File

One .PKT File – But Maybe Two (Duplicate) Toplogies

When building the content for this post, we review the examples in the book and decide whether it makes sense to supply a Packet Tracer (.pkt) file to match the example. If we choose to support an example by supplying a matching .pkt file, the .pkt file includes a topology that matches the example as much as possible. It also includes the device configurations as they should exist at the beginning of the example.

In some cases, the .pkt file shows two instances of the lab topology – one above and one below. We include two such topologies when the book example includes configuration commands, for these purposes:

  • Top/Initial: The topology at the top has the configuration state at the beginning of the example.
  • Bottom/Ending: The topology at the bottom adds the configuration per the example, so that it mimics the configuration at the end of the example.

Table of .PKT Files, by Example

 

 

Example

.PKT Includes Initial State of Example? .PKT Also Includes Ending State of Example?
Exact Match of Interface IDs?
21-1 Yes Yes Yes
21-2 Yes No Yes
21-3 Use 21-2 No Yes
21-4 Use 21-2 No Yes
21-5 Yes Yes Yes
21-6 Yes No Yes
21-7 Yes Yes Yes
21-8 Yes No N/A
21-9 Yes Yes Yes
21-10 Yes Yes Yes
21-11 Yes No Yes
21-12 Not Supplied Not Supplied N/A
21-13 Not Supplied Not Supplied N/A

Tips

The example shows the configuration for router R1. Note that the PT file, for the “initial” state devices, pre-configures similar OSPF settings for routers R2, R3, and R4.

Note: You should use the PT file for Example 21-2 for Examples 21-3 and 21-4 as well.

Note that PT does not support the show ip ospf interface brief command. Use the show ip ospf interface command (without the brief keyword) instead.

Note that PT does not support the show ip ospf interface brief command. Use the show ip ospf interface command (without the brief keyword) instead.

Note that PT does not support the show ip ospf interface brief command. Use the show ip ospf interface command (without the brief keyword) instead.

In real Cisco routers, configuration changes that impact the OSPF RID choice do not cause an immediate change in the router’s OSPF RID. Instead, to make the router choose a new RID, you must either reload the router, power off/on or use the straightforward ip ospf process EXEC command. However, be aware that CPT immediately changes the RID in most cases, not requiring the additional steps.

PT does not except the shutdown command in ospf config mode, so we did not supply PT files for these examples.

Free Play Labs - CCNA Vol 1 Chapter 20
Free Play Labs - CCNA Vol 1 Chapter 24
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Eduardo Antunes

“this files .pkt are not compatible whith this version of packet tracer” I am using PT 7.2.2

Jerry Gurrea

Hi Wendell, the command show ip ospf interface brief is unrecognized command in Packet Tracer 7.3. Is this a limitation of PT? Thanks.

Edesiri Ovwori

Thank you Wendell for all the help you have rendered. Can you please share the password to the routers in the packet tracer file for OSPF.

sana

In book example 21-9(pg 512),it is mentioned that ospf will not begin using a new RID value until the process restarts
but wen i change rid of R3 it shows the newly configured rid in show ip ospf before using the clear ip ospf process command .
so is it that it will show rid but not use it (before clearing or reloading) or is there something im missing?
also is there any other command that helps in finding duplicate RID as show ip ospf doesnt in packet tracer.
thanks

Wendell Odom

Hi Sana,
Packet Tracer acts differently from real Cisco devices in regards to the timing of when it updates the OSPF RID. Thanks for the note – I’ll add it to the growing list of Packet Tracer issues to update on various labs.
On your second question, unfortunately, there’s no easy “show all OSPF RID duplicates” process or command. Finding those can be particularly difficult when the routers are not on the same link. If the routers w/ duplicate RIDs are attempting to become neighbors, then use show ip ospf neighbors to notice odd output, or the absence of expected neighbors. Also debug ip ospf hello and debug ip ospf neighbor (one of those may not be correct, but it’s something like that.) Those are almost certainly not in PT.

Wendell Odom

For anyone who comes across this… I just updated the .pkt file to include “enable secret cisco” in the initial config for SW1.

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