IRule error

I have a basic config from Vserver to real server and this works fine with a default pool.

I have added an IRule to set rewrite to real server as follows...

when HTTP_REQUEST {

set HOST server_B.co.uk

set POOL server_B_pool

No connection to server B is made and i have this in the LTM log but i do not have any whitelists...

Sep 26 15:15:32 F5-DMZ-A1 info tmm1[17881]: Rule /Common/IR-Services <HTTP_REQUEST>: Client 192.168.100.171: GET -> server_A.com/ufs/HALS_INDEXES.eb

Sep 26 15:15:32 F5-DMZ-A1 info tmm1[17881]: Rule /Common/IR-Services <HTTP_REQUEST>: Not on whitelist. Host: server_A.com IP: 192.168.100.171

Many thanks for any advice offered.