122 lines
8.2 KiB
HTML
122 lines
8.2 KiB
HTML
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<meta name="DC.Title" content="Create IP filter rules" />
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<meta name="abstract" content="When you create a filter, you specify a rule that governs the IP traffic flow in and out of your system." />
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<title>Create IP filter rules</title>
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<body id="rzajb8a0-creating_sd"><a name="rzajb8a0-creating_sd"><!-- --></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">Create IP filter rules</h1>
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<div><p>When you create a filter, you specify a rule that governs the IP
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traffic flow in and out of your system.</p>
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<div class="section"><div class="p">The rules you define specify whether the system should permit
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or deny packets that attempt to access your system. The system directs IP
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packets based on the type of information in the IP packet headers. It also
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directs the IP packet to the action that you have specified the system to
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apply. The system discards any packets that do not match a specific rule.
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This automatic discard rule is called the <em>default deny rule</em>. Located
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at the end of the file, the default deny rule is automatically activated any
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time a packet does not match the criteria in any of the preceding rules. You
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must have at least one filter rule activated for the default deny rule to
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be active. <div class="important"><span class="importanttitle">Important:</span> When you apply rules to an interface through
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which you are configuring the iSeries™ server, it is very important
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that you permit your own workstation or that of anyone else who might be configuring
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the iSeries server.
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Failure to do so will result in a loss of communication with the iSeries server.
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If this happens, you will need to log on to the iSeries server using an interface that
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still has connectivity, such as the operators console. Use the RMVTCPTBL command
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to remove all filters on the system.</div>
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</div>
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</div>
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<div class="section"><p>Before you create your filter rules, you should determine whether
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you need to use network address translation (NAT). If you use NAT rules,
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you <em>must</em> define addresses and services. NAT is the only function that
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requires a defined address, but you can use it for other functions as well.
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If you define addresses and services, you can reduce the number of rules that
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you must create as well as minimizing the possibility of typographical errors.</p>
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</div>
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<div class="section"><div class="p">Here are some other ways you can use to minimize error and maximize
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efficiency when creating filter rules: <ul><li>Define one filter rule at a time. For example, create all the permits
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for Telnet at the same time. This way you can group associate the rules whenever
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you refer to them.</li>
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<li>Filter rules are processed in the order that they appear in the file.
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Be sure to order the rules the way you intend them to be applied when you
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create them. If the order is incorrect, your system is vulnerable to attack
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because the packets will not be processed as you intend them to be. To make
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things easier, consider the following optional actions: <ol><li>Place your filter set names in the FILTER_INTERFACE statement in the exact
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same order in which the sets are physically defined in the file.</li>
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<li>Place all filter rules in one set to avoid problems with set order.</li>
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</ol>
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</li>
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<li>Verify the syntax of each rule as you go along. This is easier and faster
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than debugging them all at once.</li>
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<li>Create set names for groups of files that are logically associated with
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each other. This is important because only one rule file can be active at
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a time. See the following example.</li>
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<li>Only write filter rules for the datagrams you want to permit. Everything
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else will be discarded by the automatic deny rule.</li>
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<li>Write rules for high traffic volume first.</li>
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</ul>
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</div>
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</div>
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<div class="section"><h4 class="sectiontitle">Example:</h4><p>Look at the <em>Create set names</em> tip
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above. You might want to allow Telnet access to a number of internal users,
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but not to all. To manage these rules easier, you can assign each of them
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the set name <samp class="codeph">TelnetOK</samp>. A second criteria can allow Telnet
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through a specific interface and block Telnet traffic from all others. In
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this case, you need to create a second set of rules that block Telnet access
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entirely. You can assign these rules the set name <samp class="codeph">TelnetNever</samp>.
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By creating set names, you make it easier to distinguish the purpose of the
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rule. It is also easier to determine which interfaces you intend to apply
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to particular sets. Use all of the tips above to ease the process of creating
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filters.</p>
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</div>
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<div class="section"><p>For instructions on how to create IP filter rules, use the Packet
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Rules Editor online help.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Next topic</h4><p>After you create your filters, you might
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want to <a href="rzajbrzajb88includessd.htm">Include files in packet rules</a> in the filter statement.
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If not, the next step is to <a href="rzajbrzajb82filterinterfacessd.htm">Define IP filter interfaces</a> to
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which the rules apply.</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="rzajbrzajbx1creatingnewrulessd.htm" title="Read the checklist that contains an overview of the tasks you must complete to ensure that your rules work properly when activated.">Configure packet rules</a></div>
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<div class="previouslink"><strong>Previous topic:</strong> <a href="rzajbrzajb8bcreatingnatrulessd.htm" title="To use network address translation (NAT), you must define nicknames for the IP addresses you intend to use.">Create NAT rules</a></div>
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<div class="nextlink"><strong>Next topic:</strong> <a href="rzajbrzajb82filterinterfacessd.htm" title="Define filter interfaces to establish the filter rules that you want the system to apply to each interface.">Define IP filter interfaces</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><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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<div class="relref"><strong>Related reference</strong><br />
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<div><a href="rzajbrzajbttrouble.htm" title="This topic provides troubleshooting advice for some common packet rules problems.">Troubleshoot packet rules</a></div>
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</div>
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</div>
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</body>
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</html>
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