93 lines
5.6 KiB
HTML
93 lines
5.6 KiB
HTML
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<meta name="DC.Title" content="Masquerade (port-mapped) NAT" />
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<meta name="abstract" content="Port-mapped network address translation (NAT) is a variation of masquerade NAT." />
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<title>Masquerade (port-mapped) NAT</title>
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<body id="rzajb4d-portnat"><a name="rzajb4d-portnat"><!-- --></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">Masquerade (port-mapped) NAT</h1>
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<div><p>Port-mapped network address translation (NAT) is a variation of
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masquerade NAT.</p>
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<p>How do they differ? In port-mapped NAT you can specify both the IP address
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and the port number to translate. This allows both your internal personal
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computer and the external workstation to initiate IP traffic. You can use
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this if the external workstation (or client) wants to access workstations
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or servers inside your network. Only IP traffic that matches both the IP address
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and the port number is allowed access. Here is how it works:</p>
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<div class="section"><h4 class="sectiontitle">Internal initiation</h4><p>When the internal personal computer
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with <em>Address 1: Port 1</em> initiates traffic to an outside workstation,
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the translating code will check the NAT rule file for <em>Address 1: Port 1</em>.
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If both the source IP address (Address 1) and the source port number (Port
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1) match the NAT rule, then NAT starts the conversation and performs the translation.
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The specified values from the NAT rule replace the IP source address and source
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port number. <em>Address 1: Port 1</em> is replaced with <em>Address 2: Port
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2</em>.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">External initiation</h4><p>An external workstation initiates
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IP traffic with the destination IP address of <em>Address 2</em>. The destination
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port number is <em>Port 2</em>. The NAT server will untranslate the datagram
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with or without an existing conversation. In other words, NAT will automatically
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create a conversation if one does not already exist. <em>Address 2: Port 2</em> is
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untranslated to <em>Address 1: Port 1</em>.</p>
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</div>
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<div class="section"><p>The following list highlights the features of masquerade port-mapped
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NAT:</p>
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<ul><li>One-to-one relationship.</li>
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<li>External and internal network initiation.</li>
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<li>The registered address the private address hides behind must be defined
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on the iSeries™ server
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performing the NAT operations.</li>
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<li>IP traffic outside of NAT operations cannot use the registered address.
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However, if this address attempts to use a port number that matches the hidden
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port in the NAT rule, then the traffic will be translated. The interface will
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be unusable.</li>
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<li>Typically the port numbers are mapped to well-known port numbers, so extra
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information is not necessary. For example, you can run an HTTP server bound
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to port 5123, then map this to the public IP and port 80. If you want to hide
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an internal port number behind another (uncommon) port number, the client
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needs to be physically told the value of the destination port number. If not,
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it is difficult for communication to occur.</li>
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</ul>
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</div>
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<div class="section"><div class="note"><span class="notetitle">Note:</span> <ul><li>You must set <samp class="codeph">MAXCON</samp> high enough to accommodate the number
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of conversations you want to use. For example, if you are using FTP, your
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personal computer will have two conversations active. You will need to set <samp class="codeph">MAXCON</samp> high
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enough to accommodate multiple conversations for each personal computer. The
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default value is <samp class="codeph">128</samp>.</li>
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<li>Masquerade NAT only supports the following protocols: TCP, UDP, and ICMP.</li>
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<li>Whenever you use NAT, you must enable IP forwarding. Use the Change TCP/IP
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Attributes (CHGTCPA) command to verify that IP datagram forwarding is set
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to <samp class="codeph">YES</samp>.</li>
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</ul>
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</div>
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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="rzajbrzajb4natsd.htm" title="Network address translation (NAT) allows you to access the Internet safely without having to change your private network IP addresses.">Network address translation (NAT)</a></div>
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</div>
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