F5 BigIP LTM – iRule Accept Only UserAgent to Hostname

The following code snippet assumes you have a wildcard virtual host within the F5 LTM device, and that you wish to only allow traffic into that virtual host if a specific user agent string is matched and that the hostname is matched.

when HTTP_REQUEST {
    if {{ [class match [HTTP::header "User-Agent"] = "Browser 2.1.0"] } and { ([string tolower [HTTP::host]] starts_with "subdomain.domain.com") }} {
        return
    } else {
        drop
    }
}

It should be modified to suit your specific requirements.