CodeIgniter session cookie domain

Question

It appears with the following cookie settings below, that cookies are set for the entire domain. For example if I was on http://subdomain.domain.com the cookie would be set

Answer 1

Domain specific cookies are only accesible on that domain. Use ".domain.com" as your cookie domain to be able to use it across all subdomains and main domain.

Answer 2

When using several codeigniter applications on subdomains it is also important to set the same $config[‘encryption_key’].