Search queries with greater-than or smaller-than

[Tobias Prinz <tobiasprinz@gmx.net>]

Hello there,

I am just starting with LDAP, but there is some basic thing that I do 
not understand and that does not make sense at all:

I have got an OpenLDAP server and it does contain data.

This search returns a bunch of results:
ldapsearch -x -v -H  ldap://localhost -b 
ou=something,dc=domainname,dc=com -LLL '(gidNumber=500)'

Yet this returns no results:
ldapsearch -x -v -H  ldap://localhost -b 
ou=something,dc=domainname,dc=com -LLL '(gidNumber>=500)'

So I invert it and this returns no results either:
ldapsearch -x -v -H  ldap://localhost -b 
ou=something,dc=domainname,dc=com -LLL '(!(gidNumber>=500))'

This simply fails (okay, I knew that, but at least I know the ones above 
are not syntax errors, because the greater-sign alone is not defined as 
a filter in RFC 1960 nor RFC 4515):
ldapsearch -x -v -H  ldap://localhost -b 
ou=something,dc=domainname,dc=com -LLL '(gidNumber>499)'

Can someone point me in the right direction, please?

Thanks in advance,
Tobias