130 APPENDIX C: AGGREGATING DEVICESSpecifying anAggregation PolicyTo aggregate devices on a particular network, it is necessary for theaggregator to be configured for that network. This is done by specifyingan aggregation policy.Once an aggregation policy has been configured, it only affects datacollected from that point on.An aggregation policy consists of three parts: a local domainspecification, a default action and a maximum device limit.Local Domain SpecificationAs well as reducing the amount of memory and disk resources required,aggregation is also an intuitive way of specifying which devices are ofinterest and should therefore be monitored closely. You can specify a listof the DNS domains which will be referred to as the local domain(s).These are the domains which you want to retain at device-specific levelfor detailed monitoring. Any device whose resolved DNS domain matchesone of these specified DNS domains, or a sub-domain of one of thespecified DNS domains, is considered to be local and will be kept in detail.Only IP addresses can have a DNS domain, and therefore only IPaddresses are considered for aggregation. Non-IP network devices arealways be considered to be local, and so will be kept in detail.You can assign DNS domains to subnets using the SubnetsDB file.Subnets can be assigned any DNS domain, but 3Com suggests that youuse local domains. If you provide a local DNS domain name for a subnet,a device in this subnet will be placed in this domain, if DNS lookup failsfor the device. This ensures that such devices appear in the correct groupwhen you use the DNS grouping.When Traffix Manager discovers a new IP device on your network, itperforms a DNS lookup for the DNS name of that device. If this lookupfails, or if your site has no DNS, Traffix Manager will check the SubnetsDBfile to see if the device is in a given subnet. If so, it will assign the DNSname of the subnet to the device. If the device is not found in SubnetsDB,then a final check is done to see if it is in the same subnet as the TraffixManager Server. If it is, the device is assigned to the subnethome-subnet and the DNS domain is set to that of the server (if it hasone). You can override this behavior by making sure that there is an entryin the SubnetsDB file for the subnet of the Traffix Manager Server. See“Using the SubnetsDB File” on page 133 for more information.
