Session handling and subdomains

[LLLLLLL]

There are lots of discussions about this topic online. My issue wasn't subdomain sessions being recognized by the primary domain (and vice versa), but rather just a subdomain handling things at all. You set something in the subdomain, refresh the page, and then the thing was unset.

 

Here's what I currently have:

session_name( "blah" );
ini_set( "session.cookie_domain", '.dev.example.com' );
session_set_cookie_params( 0, '/', '.dev.example.com', true, true );
setcookie( session_name(), session_id(), 0, '/' , '.example.com' );
session_start();

Things that were required, apparently:

1) Session name

2) setcookie

 

Now with this setup, I can do this:

start session in dev.example.com, access it in subsub.dev.example.com, go back and forth... session holds as expected.

 

But what I cannot do, is:

start session in subsub.dev.example.com, refresh page, have the session data hold.

 

So lots of questions. 

1. Obviously the most important: why doesn't a session hold when I start the session in the subsub domain?
2. Why is a session name required? (Is it?)
3. Why is setcookie required when all I want to do is start a session? (Is it?) I don't use this step if it's a single-domain type of setup.

Edited June 29, 2017 by timneu22