Keep URL after a redirect

From the description you provided, it sounds like you want to do a reverse proxy of an external website (to keep the FQDN in the client's web browser address bar the same) as opposed to a redirect? Is this correct?

If so, you will need to:

1) Create a pool containing the public IP address (or alternatively an FQDN node) of the target website

2) Enable SNAT to ensure that the return traffic routes back via the F5.

3) Replace the 301 redirect in your iRule with the following:

HTTP::header replace host "example.com"

In addition, if the target site you are wanting to proxy is using https:// then you would also need to add a server SSL profile to the VIP.