Drupal + Moodle SingleSignOn logout issues
$cookie_domain can only be set to a domain that you want the Set-Cookie header to specify. This doesn't include protocol or path, just the domain with a leading dot (e.g. ".example.com"). If you leave $cookie_domain commented out, the browser will default to the domain that you requested it on. 

If you need to access a Drupal site by IP when its cookie is set to another domain, you can create a subdomain on your hosts file that maps to the IP.

128.79.128.44 dev.example.com


Once that's saved to your hosts file, you should be able to browse to http://dev.example.com/ and have your web browser send the relevant cookies (assuming the cookies of domain are set to "example.com").