Publishers of technology books, eBooks, and videos for creative people

Home > Articles

This chapter is from the book

Exercise 23.1 Troubleshoot Network Connectivity

In this exercise, you intentionally misconfigure your network settings. You then use the macOS built-in troubleshooting tools to view symptoms and isolate the problem.

Break Your Network Settings

  1. Log in as Johnny Appleseed.

  2. Open Network preferences, then authenticate as Local Administrator.

  3. Record the currently selected location so that you can return to it at the end of the exercise.

  4. From the Location menu, choose Edit Locations.

  5. Select the Static location, then choose Duplicate Location from the Action menu below the location list.

  6. Name the new location Broken DNS, then click Done.

  7. If necessary, switch to the Broken DNS location.

  8. Click Apply.

  9. Select the primary network service (the one at the top of the left sidebar), then click Advanced.

  10. Click DNS.

  11. If there are entries in the DNS Servers list, record them so you can reenter them, then use the Remove (–) button to remove them.

  12. Click the Add (+) button under the DNS Servers list, then add the server address

    No DNS server is available at this address, which is in a block of addresses that do not legitimately appear on any network anywhere (with the exception of, which is the loopback address and outside the scope of this guide). As a result, is an invalid address.

  13. Click TCP/IP.

  14. From the Configure IPv6 menu, choose “Link-local only.”

    This prevents IPv6 from being an alternate internet connection.

  15. Click OK, then click Apply.

Observe the Problem

  1. Open Safari.

  2. Type in the address bar, then press Return.

    Safari attempts to load the webpage, but it doesn’t get far because it’s not able to reach anything. If you wait, it eventually gives up, then displays an error. Don’t wait.

  3. Quit Safari.

Check the Network Status in Network Preferences

When you have a network problem, one of the first things you should check is the network service status in Network preferences. Viewing the status lets you spot simple problems without performing detailed diagnostics.

  1. Open Network preferences.

  2. Examine the status indicators and the network services order.

    If the network service you expect to be active isn’t showing a green status indicator, something is wrong with the connection or a critical setting is missing. Examples could include a loose cable, not being joined to a Wi-Fi network, or a missing IP address.

    If the wrong service is at the top of the list, the service order was set incorrectly or unexpected services are active. In this case, the expected service has a green indicator and is at the top of the list, so you must do more troubleshooting.

Use ping to Test Connectivity

In this section, you use the ping command. You can use ping to test network connectivity and DNS resolution.

  1. Open Terminal.

    Many of the macOS troubleshooting tools are available from the command-line interface.

  2. In Terminal, type ping -c 5, followed by the domain name of the server you want to reach (

    The option -c 5 in the ping command indicates the number of ping requests to send to the host, which in this case is five.

  3. Press Return.

    After about 30 seconds, you receive a message telling you that ping couldn’t resolve The message indicates that ping wasn’t able to use DNS to look up, or resolve, the name and match it to an IP address to send the ping to. In this case, you know that the name is valid because you have used it before, so this indicates that something is wrong with DNS.

    Although this message gives you some information about the problem, it still doesn’t tell you where the problem is. It can be hard to differentiate between a DNS problem and a complete network failure. If DNS resolution is the only thing failing, it can mimic a complete failure because almost all network access starts with (and depends on) a DNS lookup. If the network is completely disconnected, most attempts to use the network fail at the DNS step, so the only symptoms are DNS errors.

    Try to reach a server by its numeric IP address to distinguish between a DNS-only problem and a complete network failure. This approach bypasses the usual DNS lookup and works even if DNS is broken.

  4. At the prompt, type ping -c 5

    This is an easy-to-remember address of a public DNS server maintained by Google.

  5. Press Return.

    This time, ping reaches its destination successfully and shows statistics for its five test pings. This tells you that your basic network connectivity is OK and that it’s likely only DNS isn’t working.

Use the host Command to Test DNS

Even though the ping error message “cannot resolve” indicates a DNS problem, try the host command to discover whether it reveals a more specific error.

  1. In Terminal, type host

    The host command is used for performing DNS lookups. You use it to convert names to IP addresses, and vice versa.

  2. Press Return.

    After about 30 seconds, you receive a message that the connection timed out and that no servers could be reached. This is the same result you got using the ping command.

Switch to Working Network Settings

  1. From the Apple menu, choose Locations, then click the Static location.

    Unlike the Broken DNS location, this location has valid settings, so your internet connectivity should be back to normal.

  2. In Terminal, type host again.

    This time the host command reaches a DNS server and finds the IP address corresponding to the domain name

    The address displayed by host may differ from the address in the figure because the Apple website is hosted by a number of servers throughout the internet and uses DNS to direct you to a server near your network location for faster access.

    If you knew the address the name should resolve to, you could verify that, but the fact that it resolved to an IP address at all is a good indication that DNS is working.

    The stdout of the host command may also display both an IPv6 address and an IPv4 address, because network services in macOS Big Sur are configured to use IPv6 automatically.

  3. Open Safari, then try browsing a website.

    This time, Safari is able to load webpages from the internet.

Peachpit Promotional Mailings & Special Offers

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


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Peachpit 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.


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.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email

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.


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


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


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 and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by Adobe 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:

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

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.


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