Here are some things to consider when selecting which data sources are to be used for autodiscovery:
If you disable the topology MIB data source, autodiscovery may not be able to find all the systems in the managed network.
IP address table MIB
By default, the IP Manager pings the addresses in networks with an 8-bit host address (254 hosts), to prevent the indiscriminate pinging of large numbers of addresses. If necessary, you can change the default 8-bit host address setting to a larger value by editing the MaximumHostBits parameter in the discovery.conf file. The IP Manager Reference Guide describes the configuration parameters in the discovery.conf file and provides instructions on modifying the parameters.
Depending on your network configuration, it can take the IP Manager a long time to ping the entire list of addresses when the MaximumHostsBits is set to a large value, such as 16 bits (more than 65,000 addresses). With a value of 24 bits, for example, it could take the IP Manager up to several hours to ping all the available addresses.
ARP table MIB
By default, this data source is not enabled because autodiscovery does not typically gain many IP addresses by using the ARP table MIB. In addition, autodiscovery does not read the ARP table MIB in hosts.