BIG-IP : iRule fails to find cookie

A few things:

1. I'd makes sure you're actually sending a cookie. If you can tcpdump on the F5 external interface, set the -Xs0 flag to show the payload.

   tcpdump -lnni 0.0 -Xs0 host x.x.x.x
   

2. Here's a really useful tool for analyzing request and response headers. You can see cookies with this as well.

   when HTTP_REQUEST {        
       foreach x [HTTP::header names] {
           log local0. "Request ($x) = [HTTP::header $x]"                
       }
   }
   when HTTP_RESPONSE {        
       foreach x [HTTP::header names] {
           log local0. "Response ($x) = [HTTP::header $x]"
       }
   }        
   

3. You can use the [HTTP::header exists ] or [HTTP::cookie exists ] mechanisms to see if a cookie actually exists in a request:

   when HTTP_REQUEST {        
       if { [HTTP::cookie exists "mycookie"] } {            
           log local0. "mycookie exists: [HTTP::cookie value mycookie]"
       }
   }