Reliable Network with SolarisTM
Peter Baer Galvin
Until recently, it was very difficult to configure a Solaris machine
to have redundant connections to a network, and to use them automatically in
case of a failure. Because of the magic of Solaris 8, the task is now easy.
If you are not IP Multipathing yet, you should be.
The Problem
Consider a Solaris host on a network. By default, it expects one network connection per subnet to which it is being attached. If it sees the same subnet on more than one interface, then one interface is used for all outbound packets, and any interface can be used by inbound packets (based on their destination addresses). Unfortunately, if the one outbound interface fails, then traffic is outbound no more.
Until recently, there were two standard methods to solve this problem. One was to buckle down and write scripts that would ping a device (say the default gateway). If the ping failed, the script could configure another interface on that subnet to handle the traffic. Of course, scripts must be debugged, supported, and updated, annoying their authors.
Alternatively, the Ethernet Trunking "Sun Consulting Special" could be purchased from Sun Professional Services. This set of scripts basically did the above work for you. Of course it cost money, and was only somewhat supported by Sun.
The problem is exacerbated by Sun servers' roles in a variety of different architectures. One example is shown in Figure 1, which shows a standard three-tier architecture, as might be found at a Web site. Most firewalls and load balancer clusters automatically manage their IP addresses during a failover. They always make an IP address available to the tier "above" them. Likewise, a database cluster has its IP addresses managed by the cluster software, which moves IPs between cluster servers as needed. The only component in this environment that does not provide such functionality is the Sun servers.
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