The checked steps as following:
(1) Firstly, check the connectivity of network between SVN2230 and AD server, After do ping test, the result is reachable.
(2) After that , check the configuration of LDAP server template in SVN2230.I find that the "Administrator DN" is configured as full DN name(the name include base DN), At the same time, the "Bind attributes to Administrator" is open yet. If configured like this, the administrator account will be incorrect. So the authentication will be failed. The configuration is shown as following: