Drop HTTP GET request based on host

I'm trying to do a simple iRule where if the HTTP request contains a particular address the connection is dropped. This is to prevent a shared webserver from being DDOS'd due to HTTP GETs to a particular site. I have the following (obviously changing domain.com to the website I want to drop traffic to):

 

 

when HTTP_REQUEST {

 

if { [HTTP::host] contains "domain.com" }{

 

TCP::release

 

return }

 

}

 

 

The iRule is being processed but it looks like the traffic isn't matching thus isn't being dropped.

 

 

Any suggestions on an error in my code or a better way to achieve this?

 

 

Thanks,

 

George