ldapsearch with filter

[Robin SP Zhang <RobinZhang@pek.destiny.com.cn>]

Hi,
    I am confused that if I search with 
ldapsearch -a always -x -h 10.16.110.102 -b "dc=syroidmanor,dc=com" -s sub
-z 20 uid=tom
,
then the server return all entries to me, why "uid=tom" can not effect the
filter?
(if I use "uid=bbb", then no result return.)

so, who can help me?