134 lines
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134 lines
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<meta name="DC.Title" content="Scenario: Adapter failover using virtual IP and proxy ARP" />
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<title>Scenario: Adapter failover using virtual IP and proxy ARP</title>
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<body id="rzajwlbvip"><a name="rzajwlbvip"><!-- --></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">Scenario: Adapter failover using virtual IP and proxy ARP</h1>
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<div><p>This solution requires you to have an external load balancing machine,
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such as IBM<sup>®</sup> eNetwork
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Dispatcher. Virtual IP addresses allow you to assign an address to the system
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rather than to a specific interface. You can define the same address to multiple
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servers, which allows many new options for load balancing.</p>
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<div class="section" id="rzajwlbvip__situation"><a name="rzajwlbvip__situation"><!-- --></a><h4 class="sectionscenariobar">Situation</h4><p>Your
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production iSeries™ handles
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data entry from both remote and LAN clients. It has the company's critical
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application on it. As the company has grown, so has its demand on the iSeries server
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and the network. Because of the growth, it has become imperative that this iSeries server
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be available on the network without an unscheduled down time. If, for any
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reason, a network adapter becomes unavailable, other network adapters on the iSeries server
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should take over and the network clients should be unaware of any failures.</p>
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</div>
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<div class="section" id="rzajwlbvip__objective"><a name="rzajwlbvip__objective"><!-- --></a><h4 class="sectionscenariobar">Objectives</h4><p>The
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concept of availability has many different aspects of redundancy and backup
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for failing components. In this scenario, the goal is to provide network availability
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to the iSeries server
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for its clients in the event of an adapter failure.</p>
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</div>
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<div class="section" id="rzajwlbvip__details"><a name="rzajwlbvip__details"><!-- --></a><h4 class="sectionscenariobar">Details</h4><p>One
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way to handle the preceding situation is to have multiple physical connections
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to the LAN from the iSeries server. Consider the following figure.</p>
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<div class="fignone"><span class="figcap">Figure 1. Adapter failover without local clients</span><br /><img src="rzajw528.gif" alt="Adapter failover without local clients" /><br /></div>
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<p>Each physical connection has a different IP address. Then you can
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assign a virtual IP address to the system. This virtual IP address is the
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IP address by which all of its clients recognize it. All remote clients (clients
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that are not physically attached to the same LAN as the iSeries server)
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communicate with the iSeries server through an external load balancing
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server such as a network dispatcher. When the IP requests from the remote
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clients go through the network dispatcher, the network dispatcher routes the
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virtual IP addresses to one of the network adapters on the iSeries server.</p>
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<p><img src="./delta.gif" alt="Start of change" />If the LAN that the iSeries server is connected to has clients,
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these clients will not use the network dispatcher to direct their locally
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bound traffic because that will unnecessarily overload the network dispatcher.
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You can create route entries on each client that are similar to the route
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tables in the network dispatcher. However, this will be impractical if the
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LAN has a large number of local clients. This situation is described in the
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following figure.<img src="./deltaend.gif" alt="End of change" /></p>
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<div class="fignone" id="rzajwlbvip__failoverlocal"><a name="rzajwlbvip__failoverlocal"><!-- --></a><span class="figcap">Figure 2. Adapter failover with
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local clients</span><br /><img src="rzajw526.gif" alt="Adapter failover with local clients" /><br /></div>
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<p>As of OS/400<sup>®</sup> V5R2,
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local clients (clients that are attached to the same LAN as the iSeries server)
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can connect to the virtual IP address of the iSeries server through ARP. This allows
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local clients to have an adapter failover solution as well. </p>
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<p><img src="./delta.gif" alt="Start of change" />In
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each case, neither local clients nor remote clients are aware of the failover
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when it occurs. The system chooses which adapters and IP addresses are the
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preferred interface for virtual IP address (VIPA) proxy Address Resolution
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Protocol (ARP) agent selection.<img src="./deltaend.gif" alt="End of change" /></p>
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<p><img src="./delta.gif" alt="Start of change" />Starting with i5/OS™ V5R4, you
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can manually select which adapters and IP addresses are to be the preferred
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interface for VIPA proxy ARP agent selection. You can select which interface
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to use by creating a preferred interface list if an adapter failure occurs.
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A preferred interface list is an ordered list of the interface addresses that
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will take over for the failed adapters. You can use either iSeries Navigator
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or the Change TCP/IP IPv4 Interface (QTOCC4IF) application programming interface
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(API) to configure a preferred interface list. The preferred interface list
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is also configurable for both virtual Ethernet and virtual IP address interfaces.<img src="./deltaend.gif" alt="End of change" /></p>
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<p><img src="./delta.gif" alt="Start of change" />Using <a href="#rzajwlbvip__failoverlocal">Figure 2</a> as
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an example, remote clients are communicating with the local system using virtual
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IP address 10.1.1.7. Suppose 10.1.1.4 is the initial local adapter being used
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for this communication, and you want 10.1.1.5 to take over if 10.1.1.4 fails.
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You also want interface 10.1.1.6 to take over if both adapters for 10.1.1.4
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and 10.1.1.5 have failed. To control the order in which these interfaces are
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used in a failover situation, you can define a preferred interface list for
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virtual IP address 10.1.1.7. In this case, it is an ordered list of interface
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addresses that consists of 10.1.1.4, 10.1.1.5, and 10.1.1.6.<img src="./deltaend.gif" alt="End of change" /></p>
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<p>The solution
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can also involve using two or more iSeries servers to support each other.
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If one of the iSeries systems
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become unavailable, then the second system can serve as a failover. The following
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figure shows the same setup using two iSeries servers.</p>
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<div class="fignone"><span class="figcap">Figure 3. Adapter
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failover with multiple iSeries and local clients</span><br /><img src="rzajw527.gif" alt="Adapter failover with multiple iSeries and local clients" /><br /></div>
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<p>The packet routing is the same as routing for a single iSeries server
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and its remote clients; however, there is a distinct difference for the local
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clients. If you have multiple iSeries servers using the same virtual
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IP address, you can only proxy for one of the iSeries servers. In this case, you will
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have the iSeries server
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with the two LAN connections serve as the proxy.</p>
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</div>
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<div class="section" id="rzajwlbvip__steps"><a name="rzajwlbvip__steps"><!-- --></a><h4 class="sectionscenariobar">Configuration
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steps</h4><p><img src="./delta.gif" alt="Start of change" />The configuration for load balancing using virtual
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IP and proxy ARP is very similar to standard TCP/IP configurations with the
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addition of a virtual TCP/IP interface.<img src="./deltaend.gif" alt="End of change" /></p>
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</div>
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</div>
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<div>
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<ol>
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<li class="olchildlink"><a href="rzajwconfiglb.htm">Configure load balancing using virtual IP and proxy ARP</a><br />
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Use these configuration steps for load balancing using virtual IP and proxy ARP.</li>
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<li class="olchildlink"><a href="rzajwcpil.htm">Create a preferred interface list</a><br />
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You can create a preferred interface list to control the order in which the local interfaces are used when an adapter failure occurs.</li>
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</ol>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzajwloadbasics.htm" title="Workload balancing is redistributing network traffic and workload of heavily accessed machines across multiple processors, multiple interface adapters, or multiple host servers.">TCP/IP workload balancing methods</a></div>
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</div>
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