When choosing credentials, consider the following:
Quick win: for quick and wide discovery coverage, try SNMPv2 credentials with a public community string first.
Tip: You can find community strings in use at your site by looking in network device configurations or consulting your site's documentation.
For Windows host devices, add Windows credentials.
Some Linux/UNIX and Windows hosts might need an SNMP agent (service) running to fetch SNMP statistic values for initial discovery.
From most Windows versions, you can add this from the Windows Turn Windows Features On or Off dialog.
From Linux, install the SNMP package from your respective package manager (yum, apt-get, zypper).
Add SSH credentials for Linux/UNIX host devices.
Apply VMware credentials to vCenter hosts.
When reapplying existing Hyper-V host credentials, an additional step is needed to distribute the new credentials to the VMs. For details, see Windows credential for Hyper-V.