Unrecognized database type (ldap)

["Raffaele Viola" <raffovi@gmail.com>]

Hi all,
I want to create a ldap type batabase in my ldap server as explained in the man 
SLAPD-LDAP(5).

database ldap (

man: This  backend  acts  as  a proxy to forward incoming requests to another LDAP server.)
suffix "dc=RAFFO,dc=IT"
uri    "ldap://151.98.181.93/dc=RAFFO,dc=IT
"
rootdn ""cn=Manager,dc=RAFFO,dc=IT"

rootpw   secret
binddn "cn=Manager,dc=RAFFO,dc=IT"

bindpw secret
lastmod   off

but it doesn't work because I get this error:

Unrecognized database type (ldap)

Can you help me thanks
Raffo