You can use local authentication as a fallback in the event that the LDAP server is unreachable. The local authentication plugin is called userManager.
Verify that the userManager plugin is available:
Go to the following URL to access the Zope Management Interface (ZMI):
In the Name column, click Plugins.
Click Authentication Plugins.
Make sure that your LDAP plugin is first in the list of Active Plugins. (The userManager plugin must be below it.)
Create a user with fallback capabilities. For example, to allow an LDAP user named "zenoss-user" to log in when the LDAP server is down:
Go to Advanced > Settings > Users > Add New User.
Create a user named "zenoss-user."
You must create this account before the user logs in with the LDAP credentials. The password defined when creating the account in Zenoss will be valid even when the LDAP server is down.