Which identity source could be used to query the Active Directory if Cisco ISE were to get disconnected from the domain?

The correct answer is LDAP. When Cisco Identity Services Engine (ISE) needs to interact with Active Directory (AD), it typically does so using Lightweight Directory Access Protocol (LDAP). If Cisco ISE becomes disconnected from the domain, querying Active Directory would still rely on LDAP as it is specifically designed for accessing and maintaining distributed directory information services over an internet protocol network.

LDAP allows for the querying of user credentials and other directory data without requiring continuous connectivity to the AD domain. This means that even if ISE loses its connection, it can still perform queries on the configuration it has on hand and utilize LDAP's capabilities to access necessary identity information.

In contrast, SAML is focused on web-based single sign-on (SSO) and might not be applicable for querying traditional directory data in the same way. RADIUS operates as a protocol for authentication, authorization, and accounting but is not inherently designed for querying directory information. ODBC, while relevant for database connectivity, is not relevant in the context of querying Active Directory for user identity information. Thus, LDAP stands out as the most suitable option.