Introduction

The management domain is the set of subnets that NNM manages. Within these subnets NNM will flex its considerable autodiscovery muscles and attempt to manage every device that passes through the discovery filter. NNM ignores subnets that are not in the management domain. That means a remote network device won’t be discovered even when the NNM system is otherwise aware of it, which it might be if a network administrator telnets to it.

Defining the management domain begins with an understanding of the communities of interest in the network. Users and the equipment they use are located in IP subnets somewhere on the network, so these subnets need to be identified. This helps determine which subnets should be included in the management domain and what parameters should be included in the discovery filter.

Geographies often align with business entities, so simply listing all the subnets in the geography defines the management domain. This is by far the most common arrangement. Listing all the routers in the geography in the seedfile is usually an excellent first approximation to defining the management domain.

Estimating the size of a management domain means determining how many managed devices are in it. This is a critical estimate because the NNM system must be adequately sized for this number of managed devices. Several methods for making this estimate are reviewed in this chapter.

When the initial management domain is defined, you need a strategy for defining and discovering it in anticipation of first discovery. This means gathering community strings, SNMP SysObjectID, a.k.a. system object identifiers (OID), and obtaining icons for managed devices. It also means being prepared for a wide range of discovery difficulties, including bad SNMP agents and crashing NNM daemons.

Armed with this strategy, you can prepare your configuration files for first discovery. These files include the netmon seedfile, the discovery filter, the DHCP filter, the xnmsnmpconf command line input file of community strings, the polling parameters for xnmpolling, and the netmon.noDiscover file.