blocking access to sql server from particular IP

Hi I wan to to block to sql server (SQL2005) from particular IP

I created trigger

CREATE TRIGGER [tgr_blocker]
ON ALL SERVER
FOR LOGON
AS
BEGIN

IF isnull((SELECT client_net_address FROM sys.dm_exec_connections WHERE session_id = @@SPID),'') = '111.2.2.123'
ROLLBACK;

END;

trigger detect   '111.2.2.123'  but also deny access to SOME other IP

(20 diffrent users from diffrent ip conencted all the time, but 3-4 get access denied if trigger enabled)

Message
Logon failed for login 'MYCORP\blockedUser' due to trigger execution. [CLIENT: 111.2.2.123]--this is how it should be

Message
Logon failed for login 'MYCORP\userWhoshouldAccessServer' due to trigger execution. [CLIENT: 111.3.3.567]--this user denied access

What is missing in my trigger ?