Home > Articles > Implementing OSPF for IPv4

Implementing OSPF for IPv4

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Nov 19, 2016.

Contents

  1. Foundation Topics
  2. Review Activities

Chapter Description

In this sample chapter from CCNA Routing and Switching ICND2 200-105 Official Cert Guide Academic Edition,author Wendell Odom covers implementation details for Open Shortest Path First Version 2 (OSPFv2) —that is, OSPF as used for IPv4. This chapter looks at how to configure and verify a variety of OSPFv2 features.

Review Activities

Chapter Summary

  • The OSPF network command is used to match the IP addresses that are configured on the interfaces. Those that match are inserted into the OSPF process.

  • The OSPF network command uses wildcard masks to control which bits in an octet are matched.

  • The show ip ospf neighbor command can be used to find information about any OSPF neighborships, including the interface, the state, the neighbor’s address, and the neighbor’s router ID.

  • To select a router ID for OSPF, a router goes through a process. When a router ID has been found, the process stops. The process is any value configured with the router-id command; the highest configured IPv4 address of any enabled loopback interface; and the highest configured IPv4 address of any physically up (up/up or up/down) physical interface.

  • An OSPF interface configured as passive will quit sending OSPF Hello messages, will ignore any received Hello messages, and will not form any neighborships.

  • The only OSPF router configured into multiple areas is an Area Border Router (ABR).

  • The show ip ospf interface [type number | brief] command can be used to display which interfaces are enabled into the OSPF process.

  • The show ip ospf neighbor [type number] command can be used to display any OSPF neighborships.

  • The show ip ospf database command can be used to display the OSPF LSDB.

  • The show ip route [ospf | subnet mask] command can be used to display OSPF routes in the current routing table.

  • The show ip protocols and show ip ospf interface [brief] commands can be used to display which areas are configured on a device.

  • The OSPF default-information originate command is used along with a configured static default route to advertise a default route into OSPF.

  • OSPF uses three rules to set interface costs: setting the cost explicitly with the ip ospf cost cost command, changing the interface bandwidth with the bandwidth bandwidth command, or changing the reference bandwidth with the auto-cost reference-bandwidth reference-bandwidth command.

  • The output of the show ip protocols and show ip ospf interface commands will differ depending on whether OSPF was configured with the old (network) or new (interface commands) configuration style.

Review Questions

  1. Which of the following network commands, following the command router ospf 1, tells this router to start using OSPF on interfaces whose IP addresses are 10.1.1.1, 10.1.100.1, and 10.1.120.1?

    1. network 10.0.0.0 255.0.0.0 area 0

    2. network 10.0.0.0 0.255.255.255 area 0

    3. network 10.0.0.1 0.0.0.255 area 0

    4. network 10.0.0.1 0.0.255.255 area 0

  2. Which of the following network commands, following the command router ospf 1, tells this router to start using OSPF on interfaces whose IP addresses are 10.1.1.1, 10.1.100.1, and 10.1.120.1?

    1. network 10.1.0.0 0.0.255.255 area 0

    2. network 10.0.0.0 0.255.255.0 area 0

    3. network 10.1.1.0 0.x.1x.0 area 0

    4. network 10.1.1.0 255.0.0.0 area 0

    5. network 10.0.0.0 255.0.0.0 area 0

  3. Which of the following commands list the OSPF neighbors off interface serial 0/0? (Choose two answers.)

    1. show ip ospf neighbor

    2. show ip ospf interface brief

    3. show ip neighbor

    4. show ip interface

    5. show ip ospf neighbor serial 0/0

  4. Routers R1, R2, and R3 are internal routers in areas 1, 2, and 3, respectively. Router R4 is an ABR connected to the backbone area (0) and to areas 1, 2, and 3. Which of the following answers describes the configuration on Router R4, which is different from the other three routers, that makes it an ABR?

    1. The abr enable router subcommand.

    2. The network router subcommands refer to a single nonbackbone area.

    3. The network router subcommands refer to multiple areas, including the backbone.

    4. The router has an interface in area 0, whereas an OSPF neighbor’s interface sits in a different area.

  5. An engineer connects to Router R1 and issues a show ip ospf neighbor command. The status of neighbor 2.2.2.2 lists FULL/BDR. What does the BDR mean?

    1. R1 is an Area Border Router.

    2. R1 is a backup designated router.

    3. Router 2.2.2.2 is an Area Border Router.

    4. Router 2.2.2.2 is a backup designated router.

  6. An engineer migrates from a more traditional OSPFv2 configuration that uses network commands in OSPF configuration mode to instead use OSPFv2 interface configuration. Which of the following commands configures the area number assigned to an interface in this new configuration?

    1. The area command in interface configuration mode

    2. The ip ospf command in interface configuration mode

    3. The router ospf command in interface configuration mode

    4. The network command in interface configuration mode

  7. Which of the following configuration settings on a router does not influence which IPv4 route a router chooses to add to its IPv4 routing table when using OSPFv2?

    1. auto-cost reference-bandwidth

    2. delay

    3. bandwidth

    4. ip ospf cost

Chapter Review

One key to doing well on the exams is to perform repetitive spaced review sessions. Review this chapter’s material using either the tools in the book, DVD, or interactive tools for the same material found on the book’s companion website. Refer to the “Your Study Plan” element for more details. Table 8-4 outlines the key review elements and where you can find them. To better track your study progress, record when you completed these activities in the second column.

Table 8-4 Chapter Review Tracking

Review Element

Review Date(s)

Resource Used:

Review key topics

 

Book, DVD/website

Review key terms

 

Book, DVD/website

Answer chapter review questions

 

Book, PCPT

Do labs

 

Blog

Review Config Checklists

 

Book, DVD/website

Review command tables

 

Book

Review All the Key Topics

key_topic.jpg

Table 8-5 Key Topics for Chapter 8

Key Topic Element

Description

Page Number

List

Example OSPF wildcard masks and their meaning

187

Example 8-4

Example of the show ip ospf neighbor command

189

List

Rules for setting the router ID

191

List

Actions IOS takes when an OSPF interface is passive

192

Example 8-14

Example of a multiarea OSPFv2 configuration

196

Figure 8-5

Popular OSPF show commands and their general purposes

198

Example 8-15

Example of the show ip ospf interface brief showing interfaces in multiple areas

198

Figure 8-6

Actions taken by the OSPF default-information originate command

201

List

Rules for setting OSPF interface cost

204

Example 8-22

Differences in show ip ospf interface output with OSPF interface configuration

207

Key Terms You Should Know

  • reference bandwidth

  • interface bandwidth

  • maximum paths

Command References

Tables 8-6 and 8-7 list configuration and verification commands used in this chapter. As an easy review exercise, cover the left column in a table, read the right column, and try to recall the command without looking. Then repeat the exercise, covering the right column, and try to recall what the command does.

Table 8-6 Chapter 8 Configuration Command Reference

Command

Description

router ospf process-id

Enters OSPF configuration mode for the listed process.

network ip-address wildcardmask area area-id

Router subcommand that enables OSPF on interfaces matching the address/wildcard combination and sets the OSPF area.

ip ospf process-id area areanumber

Interface subcommand to enable OSPF on the interface and to assign the interface to a specific OSPF area.

ip ospf cost interface-cost

Interface subcommand that sets the OSPF cost associated with the interface.

bandwidth bandwidth

Interface subcommand that directly sets the interface bandwidth (Kbps).

auto-cost reference-bandwidth number

Router subcommand that tells OSPF the numerator in the Reference_bandwidth / Interface_bandwidth formula used to calculate the OSPF cost based on the interface bandwidth.

router-id id

OSPF command that statically sets the router ID.

interface loopback number

Global command to create a loopback interface and to navigate to interface configuration mode for that interface.

maximum-paths number-ofpaths

Router subcommand that defines the maximum number of equalcost routes that can be added to the routing table.

passive-interface type number

Router subcommand that makes the interface passive to OSPF, meaning that the OSPF process will not form neighbor relationships with neighbors reachable on that interface.

passive-interface default

OSPF subcommand that changes the OSPF default for interfaces to be passive instead of active (not passive).

no passive-interface type number

OSPF subcommand that tells OSPF to be active (not passive) on that interface or subinterface.

default-information originate [always]

OSPF subcommand to tell OSPF to create and advertise an OSPF default route, as long as the router has some default route (or to always advertise a default, if the always option is configured).

Table 8-7 Chapter 8 EXEC Command Reference

Command

Description

show ip ospf

Lists information about the OSPF process running on the router, including the OSPF router ID, areas to which the router connects, and the number of interfaces in each area.

show ip ospf interface brief

Lists the interfaces on which the OSPF protocol is enabled (based on the network commands), including passive interfaces.

show ip ospf interface [type number]

Lists a long section of settings, status, and counters for OSPF operation on all interfaces, or on the listed interface, including the Hello and Dead Timers.

show ip protocols

Shows routing protocol parameters and current timer values.

show ip ospf neighbor [type number]

Lists brief output about neighbors, identified by neighbor router ID, including current state, with one line per neighbor; optionally, limits the output to neighbors on the listed interface.

show ip ospf neighbor neighbor-ID

Lists the same output as the show ip ospf neighbor detail command, but only for the listed neighbor (by neighbor RID).

show ip ospf database

Lists a summary of the LSAs in the database, with one line of output per LSA. It is organized by LSA type (first type 1, then type 2, and so on).

show ip route

Lists all IPv4 routes.

show ip route ospf

Lists routes in the routing table learned by OSPF.

show ip route ip-address mask

Shows a detailed description of the route for the listed subnet/mask.

clear ip ospf process

Resets the OSPF process, resetting all neighbor relationships and also causing the process to make a choice of OSPF RID.

Answers to the Review Questions:

  1. B

  2. A

  3. A, E

  4. C

  5. D

  6. B,

  7. B

Cisco Press Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Cisco Press and its family of brands. I can unsubscribe at any time.

Overview

Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Cisco Press products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@ciscopress.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security

Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children

This site is not directed to children under the age of 13.

Marketing

Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out

Users can always make an informed choice as to whether they should proceed with certain services offered by Cisco Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.ciscopress.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links

This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020