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HP OpenVMS Systemsask the wizard |
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The Question is: We have a OpenVMS 7.1 cluster of two VAX 4108's running UCX 4.2. I want to enable cluster load balancing from PCs attaching to the cluster via TCP/IP using the alias. I have managed to get this working within the cluster itself and from other VAX's in the same domain. The only way I could do this was to configure the B IND resolver on each node and remove the cluster alias record from the host database, allowing it to be found in the BIND database. I have used UCX$METRICVIEW and the BIND debug logicals to determine that it is working as expected. How is it possible to set this up for access from PCs? The Answer is : What application are you using on the PC systems? If the application is a normal Internet application (SMTP and POP mail, LPD printing, TELNET, FTP, etc.), then a PC client receives the same benefit from nameserver-based load balancing as would any other client. On the other hand, if you are using PATHWORKS (Advanced Server), then effective cluster load balancing requires somewhat more effort. The Wizard has been told the PATHWORKS group is planning to address this in a future release. Meanwhile, it may be possible to achieve some load balancing through careful configuration.) The key to handling load balancing in PATHWORKS (Advanced Server) is how the client resolves the netbios name specified. As long as all clients are in the same subnet as the PATHWORKS cluster (hardly a common scenario), then allowing clients to send UPD broadcasts to resolve the PATHWORKS cluster alias name (so each cluster member running PATHWORKS sees the name request) will get you load balancing (based solely on PATHWORKS' load-balancing scheme) and will also provide fairly transparent failover. When you expand to a WAN environment, the broadcast approach gets rather more messy, obviously. The PATHWORKS cluster alias name is not tied to any IP address. In order for remote systems to use the alias name, that name needs to be defined in some (NetBIOS) name table (because the broadcasts won't pass the routers), statically mapping the name to a specific address. Some customers are using the UCX cluster impersonator address for this purpose - but this pretty much eliminates any load-balancing. A similar problem arises for WINS clients - how do you define the PATHWORKS cluster alias name in the WINS database when there is no IP address assigned to it? Many customers define a static, multi-homed entry, including the IP address of each cluster member running PATHWORKS in the list. But this isn't bullet-proof either (but seems to be the least painful approach), especially for Microsoft Windows 95 clients. Finally, don't even try using the BIND "load-balancing" mechanisms and setting the Windows clients to resolve NetBIOS names via DNS. Well, perhaps if you have all Windows 95 clients -- this approach is rather problematic for Windows NT clients, at best. In fact, most of it doesn't work due to the different manner in which Windows NT clients, when resolving a NetBIOS name via a DNS query, attempt to connect to the PATHWORKS server.
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