LDAP in Mac OS X Server
Subject:   LDAP Authentication (10.3.4 Server & Client)
Date:   2004-06-18 12:27:02
From:   highthoughts
Response to: LDAP Authentication (10.3.4 Server & Client)

i have seen similar issues with auth to a mac osX server running both netinfo and openldap when spanning tree is turned on. i would disable spanning tree on your switches and try the auth again.
the reason it works with the dumb hub is simply that is doesn't support spanning tree