Home > Articles > Networking > Routing & Switching

Network Security First-Step: Firewalls

  • Print
  • + Share This
This chapter dissects a firewall’s duties to understand what makes a firewall operate and how it does its job.
This chapter is from the book

Courage is resistance to fear, mastery of fear—not absence of fear.” —Mark Twain

By the end of this chapter, you should know and be able to explain the following:

  • Who needs a firewall, and why firewalls are used to protect network resources
  • How a firewall is a technological expression of your organization’s written security policy
  • When a DMZ is appropriate and the security benefits you gain by deploying a firewall with a DMZ

Answering these key questions enables you to understand the overall characteristics and importance of network security. By the time you finish this book, you will have a solid appreciation a firewall’s role, its issues, how it works, and why it is so important to the security of your network.

The Internet is an exciting and wonderful place to browse and explore. It has been likened to the Wild West, The Great Frontier, and other grandiose achievements of mankind. In reality, the World Wide Web is merely a collection of routers and servers that make up the largest WAN in recorded history. This collection of networking gear provides mail servers, websites, and other information storage and retrieval systems and is all connected to the Internet and accessible to every person who is also connected. It has even been said that the Internet will contain the collective institutional knowledge of mankind, eventually. Entire books have been written on the Internet’s potential and its impact on our lives—rest assured that this is not one of those books. But it does make you ponder just how much of your life is out there already that you might or might not be aware of.

We are concerned with a network’s security, so we must ask what kinds of safeguards are in place to protect such an unbelievable amount of information. Is there some organization that polices the Internet much in the same way that law enforcement cruises the highways? How about a governmental agency that snoops around and double-checks every possible device connected to the Internet? The answer to these questions is no; there is no unifying organization responsible for protecting the Internet.

The job of securing and protecting the gateways of the Internet’s knowledge is left up to the person or persons responsible for the Internet connection and network hardware/software, such as the router, firewall, switch, server operating systems, application, and so on. This person or persons are tasked with the job to ensure that hackers (the bad guys) do not make a mess of the carefully stored and catalogued information in question. And just how can you protect a website, mail server, FTP server, or other information sources accessible from the Web?

The answer is one word—firewall. The sole purpose of these dedicated hardware devices is to provide security for your network. A firewall is a security device that sits on the edge of your Internet connection and functions as an Internet border security officer. It constantly looks at all the traffic entering and exiting your connection, waiting for traffic it can block or reject in response to an established rule. The firewall is the law and protection in the lawless wild wild web. A firewall is ever vigilant in its mission to protect the network resources connected to it.

The Internet has made so much information available to individual users as, over the years, access to this information has evolved from an advantage to an essential component for both individuals and businesses. However, making your information available on the Internet can expose critical or confidential data to attack from everywhere and anywhere in the world—the Internet is literally a worldwide network. This means that, when you connect to the Internet in Madison, Mississippi, you can be subject to attacks from Europe, Asia, and Russia—literally any device connected to the Internet anywhere on the earth, which is kind of disturbing. Firewalls can help protect both individual computers and corporate networks from hostile attacks from the Internet, but you must understand your firewall to correctly use it.

This 24-hour/365-day-a-year “electronic Robocop” has an important job: to keep the bad guys out and let the good guys get to the resources they need to do their jobs. Sounds simple, right? On paper, it sounds like a walk in the park, but in reality, properly configuring a firewall is far from easy.

In some cases, a badly configured or feature-inadequate firewall can be worse than no firewall at all. This is difficult to believe, isn’t it? Nonetheless, it is true. This chapter dissects a firewall’s duties to understand what makes a firewall operate and how it does its job.

Firewall Frequently Asked Questions

Before looking at the overall operation of a firewall, the following sections examine and answer some of the fundamental questions about them.

Who Needs a Firewall?

This is perhaps the most frequently asked security question. If you plan to connect to the Internet, you need a firewall. It does not matter whether you connect from home or your company connects—you need a firewall, period! The increased penetration of broadband Internet services to the home and their always-on Internet connections make home security even more important.

Why Do I Need a Firewall?

You read about security threats in the papers or hear about them on the evening news almost every day: viruses, worms, denial-of-service (DoS) attacks, hacking, and new vulnerabilities to your computer. For example, Code Red, Slammer, and other threats/vulnerabilities. are changing with the prevalence of malware and botnets.

It is no secret that hackers are out there, and they are out to get you. Often, you do not know who they are, but you do know where they are and where you do not want them to be (in your network). Like pirates of old who roamed the seas, hackers freely roam the open expanses of the Internet. You do not want them to enter your network and roam among the computers that connect to it, and that is where a firewall becomes a requirement.

You know that you must protect your network from these attackers, and one of the most efficient methods of protecting your network is to install a firewall. By default, any good firewall prevents network traffic from passing between the Internet and your internal network. This does not mean that the firewall can stop all traffic—that defeats the purpose of being on the Internet. It does mean that the firewall is configured to allow only web browsing (HTTP/port 80) to access it from the Internet. Along the way, the firewall provides Stateful Packet Inspection (SPI) rules to every incoming packet (as discussed previously in Chapter 2, “Security Policies.”)

The alternative to having a firewall is allowing every connection into your network from anyone, anywhere—there wouldn’t be any sort of packet inspection to determine whether an attack is hidden within one of the incoming packets. Not having a firewall is ill-advised and will make your organization wide open to everyone on the Internet.

Do I Have Anything Worth Protecting?

I often hear people say, “I understand that if I had something worth protecting, I would definitely need a firewall. However, I do not have anything an attacker would want, so why should I worry about a firewall?”

Networks and their resources are important to the way our society conducts business and operates. In practical terms, this means that there is value to your network and having it effectively operate. This increased role of networks means that you definitely have something worth protecting to some degree, as documented in the following list:

  • Downstream liability: This sounds like a confused Bassmasters fishing show title, but it is perhaps the next big step in the legal evolution of the Internet. Downstream liability involves allegations that an attacker has taken control of a target computer (yours) and used it to attack a third party. Assume that it is your company’s computer that has been compromised by a hacker. Your company’s failure to protect its own systems has resulted in the damaging of a third party; the attacker used your computer as a weapon against the third party. Your company is therefore negligent due to lack of due diligence because it failed to protect against reasonable risks—specifically, no firewall was in place, or it was improperly configured, which is just as bad.

    The prudent person’s responsibility for security here is to use reasonable care. You can find a more detailed definition in Prosser, Wade, and Schwartz’s Cases and Materials on Torts: “...requiring the actor to conform to a certain standard of conduct, for the protection of others against unreasonable risks.” Who says Hollywood liberalism doesn’t contribute to society?

  • Lost data: You have probably heard the stories of companies that lost all their business data in hurricanes such as Katrina or the September 11 attacks, and many companies did not recover. What if your company experienced the same loss of data because you did not have a firewall and an attacker deleted your data because he could? What would happen to your business? Would it cost money to re-create everything? Would you suffer lost sales? Would you still be employed the next day?
  • Compromise confidential data: Every organization has data it considers confidential and, if lost, might cause financial problems, legal difficulties, or extreme embarrassment. These things might be caused by the loss of customer information such as credit card numbers, secret plans for the new weight loss formula, or secret product plans that end up in the hands of a competitor. The list goes on, and when you have been hacked, you must assume the worst. Perhaps this is why most cybercrimes go unreported—it is embarrassing, and admitting to being hacked is a sign of weakness that could affect the reputation and brand of a company.
  • Network downtime: Have you ever gone to an ATM machine or a grocery store to get cash and paid with your cash card in the swipe card readers? The networks enabling these devices to operate usually work fine; however, if they were not protected, an attacker might cause them to go down. The loss of revenue from these networks can quickly grow if they are unavailable. Downtime is the bane of any network, and a cost is always associated with these types of events.

Ultimately, everyone has something worth protecting, and failure to do so is ill-advised; it is just a matter of time before something happens. The next question is, “What does a firewall do to protect my network?”

What Does a Firewall Do?

A firewall examines traffic as it enters one of its interfaces and applies rules to the traffic—in essence, permitting or denying the traffic based on these rules. Figure 7-1 shows a firewall filters both inbound and outbound traffic.

Figure 7-1

Figure 7-1 Firewall in Operation

Firewalls use access control lists (ACLs) to filter traffic based on source/destination IP addresses, protocol, and the state of a connection. In other words, normally you might not allow FTP/21 into your network (via the firewall), but if a user inside your network begins an FTP session out to the Internet, it is allowed because the session was established from inside the network. By default, firewalls trust all connections to the Internet (outside) from the trusted internal network (inside).

A firewall can also log connection attempts with certain rules that might also issue an alarm if they occur. Finally, firewalls enable you to perform Network Address Translation (NAT) from internal private IP addresses to public IP addresses. The section “Firewall Operational Overview” discusses the roles of a firewall; however, here you can tie the firewalls back to Chapter 2’s security policy discussions by examining how a firewall enforces your security policy.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT 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 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@informit.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 InformIT. 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.informit.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