149 lines
9.2 KiB
HTML
149 lines
9.2 KiB
HTML
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Firewalls" />
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<meta name="abstract" content="A firewall is a blockade between a secure internal network and an untrusted network such as the Internet." />
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<title>Firewalls</title>
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</head>
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<body id="rzaj4fwfirewallconcept"><a name="rzaj4fwfirewallconcept"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Firewalls</h1>
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<div><p>A firewall is a blockade between a secure internal network and
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an untrusted network such as the Internet.</p>
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<p>Most companies use a firewall to connect an internal network safely to
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the Internet, although you can use a firewall to secure one internal network
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from another also.</p>
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<p>A firewall provides a controlled single point of contact (called a chokepoint)
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between your secure internal network and the untrusted network. The firewall:</p>
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<ul><li>Lets users in your internal network use authorized resources that are
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located on the outside network.</li>
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<li>Prevents unauthorized users on the outside network from using resources
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on your internal network.</li>
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</ul>
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<p>When you use a firewall as your gateway to the Internet (or other network),
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you reduce the risk to your internal network considerably. Using a firewall
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also makes administering network security easier because firewall functions
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carry out many of your security policy directives.</p>
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<div class="section"><h4 class="sectiontitle">How a firewall works</h4><p>To understand how a firewall
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works, imagine that your network is a building to which you want to control
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access. Your building has a lobby as the only entry point. In this lobby,
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you have receptionists to welcome visitors, security guards to watch visitors,
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video cameras to record visitor actions, and badge readers to authenticate
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visitors who enter the building.</p>
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<p>These measures may work well to control
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access to your building. But, if an unauthorized person succeeds in entering
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your building, you have no way to protect the building against this intruder's
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actions. If you monitor the intruder's movements, however, you have a chance
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to detect any suspicious activity from the intruder.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Firewall components</h4><p>A firewall is a collection of
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hardware and software that, when used together, prevent unauthorized access
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to a portion of a network. A firewall consists of the following components:</p>
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<ul><li><img src="./delta.gif" alt="Start of change" />Hardware. Firewall hardware typically consists of a separate
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computer or device dedicated to running the firewall software functions.<img src="./deltaend.gif" alt="End of change" /></li>
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<li>Software. Firewall software provides a variety of applications. In terms
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of network security, a firewall provides these security controls through a
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variety of technologies: <ul><li>Internet Protocol (IP) packet filtering</li>
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<li>Network address translation (NAT) services</li>
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<li>SOCKS server</li>
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<li>Proxy servers for a variety of services such as HTTP, Telnet, FTP, and
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so forth</li>
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<li>Mail relay services</li>
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<li>Split Domain name services (DNS)</li>
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<li>Logging</li>
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<li>Real-time monitoring</li>
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</ul>
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<div class="note"><span class="notetitle">Note:</span> Some firewalls provide virtual private networking (VPN) services
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so that you can set up encrypted sessions between your firewall and other
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compatible firewalls.</div>
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</li>
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</ul>
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</div>
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<div class="section"><h4 class="sectiontitle">Using firewall technologies</h4><p>You can use the firewall
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proxy servers, SOCKS server, or NAT rules to provide internal users with safe
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access to services on the Internet. The proxy and SOCKS servers break TCP/IP
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connections at the firewall to hide internal network information from the
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untrusted network. The servers also provide additional logging capabilities.</p>
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<p>You
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can use NAT to provide Internet users with easy access to a public server
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behind the firewall. The firewall still protects your network because NAT
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hides your internal IP addresses.</p>
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<p>A firewall also can protect internal
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information by providing a DNS server for use by the firewall. In effect,
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you have two DNS servers: one that you use for data about the internal network,
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and one on the firewall for data about external networks and the firewall
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itself. This allows you to control outside access to information about your
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internal systems.</p>
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<p>When you define your firewall strategy, you may think
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it is sufficient to prohibit everything that presents a risk for the organization
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and allow everything else. However, because computer criminals constantly
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create new attack methods, you must anticipate ways to prevent these attacks.
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As in the example of the building, you also need to monitor for signs that,
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somehow, someone has breached your defenses. Generally, it is much more damaging
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and costly to recover from a break-in than to prevent one.</p>
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<p>In the case
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of a firewall, your best strategy is to permit only those applications that
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you have tested and have confidence in. If you follow this strategy, you must
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exhaustively define the list of services you must run on your firewall. You
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can characterize each service by the direction of the connection (from inside
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to outside, or outside to inside). You should also list users who you will
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authorize to use each service and the machines that can issue a connection
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for it.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">What a firewall can do to protect your network</h4><p><img src="./delta.gif" alt="Start of change" />You
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install a firewall between your network and your connection point to the Internet
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(or other untrusted network). The firewall then allows you to limit the points
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of entry into your network. A firewall provides a single point of contact
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(called a chokepoint) between your network and the Internet. Because you have
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a single point of contact, you have more control over which traffic to allow
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into and out of your network.<img src="./deltaend.gif" alt="End of change" /></p>
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<p>A firewall appears as a single address
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to the public. The firewall provides access to the untrusted network through
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proxy or SOCKS servers or network address translation (NAT) while hiding your
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internal network addresses. Consequently, the firewall maintains the privacy
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of your internal network. Keeping information about your network private is
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one way in which the firewall makes an impersonation attack (spoofing) less
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likely.</p>
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<p><img src="./delta.gif" alt="Start of change" />A firewall allows you to control traffic into and
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out of your network to minimize the risk of attack to your network. A firewall
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securely filters all traffic that enters your network so that only specific
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types of traffic for specific destinations can enter. This minimizes the risk
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that someone might use TELNET or file transfer protocol (FTP)
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to gain access to your internal systems.<img src="./deltaend.gif" alt="End of change" /></p>
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</div>
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<div class="section"><h4 class="sectiontitle">What a firewall cannot do to protect your network</h4><p>While
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a firewall provides a tremendous amount of protection from certain kinds of
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attack, a firewall is only part of your total security solution. For instance,
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a firewall cannot necessarily protect data that you send over the Internet
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through applications such as SMTP mail, FTP, and TELNET. Unless you choose
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to encrypt this data, anyone on the Internet can access it as it travels to
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its destination.</p>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzaj45zgiptraffic.htm" title="Use this information to learn about the network level security measures that you should consider using to protect your internal resources.">Network security options</a></div>
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</div>
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</div>
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</body>
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</html> |