Description:
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I have a small app in which I would like to use sessions, no different than many others I have written in the past.  However, on this one I would like to set the cookie domain to a domain as opposed to a host.  However, when I do so, it seems to not work in Mozilla and IE (it does however work in konqueror).  I have tried setting the cookie_domain through ini_set and through session_set_cookie_params and through setcookie, all with the same result.  If I don't set the domain, the cookie works fine (although only for that host of course).  I have searched high and low for an answer to this but have been unable to turn up anything.

Reproduce code:
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$cookie_domain = '.my.sub.domain';

// Set session parameters and start session
ini_alter("session.gc_maxlifetime", "172800");
ini_alter( "session.entropy_file","/dev/random");
ini_alter( "session.entropy_length","512");
ini_set( "session.name",$session_name);
ini_set( "session.cookie_domain", $cookie_domain);
session_start();


Expected result:
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I expect that the cookie will be set on the browser.  It does get set in konqueror, but not in any other browser that I have access to (mozilla running in both linux and windows, and ie)

Actual result:
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It never appears when I try to set the cookie_domain.  If I don't set it, the cookie appears normally.  Additionally, I can turn on the feature in mozilla to ask whether or not to accept each cookie it receives, I never even get the question when the domain is set.  Note that the behavior is the same if I set the cookie_domain to the hostname as well.