setting cross-subdomain cookies accessible to a sub-subdomain?

I've set a coo开发者_开发技巧kie with domain of .example.com. It is available for every first-level subdomain on my site, as it should be.

It is not, however, available on nth level subdomains, i.e. sub.subdomain.example.com and too.many.subdomains.subdomain.example.com don't see the cross-subdomain cookie while subdomain.example.com does. Is there any fix for this?

The client seems not to follow the rules specified in the rfc. IE fails when there's an underscore in the domain name.

See https://www.rfc-editor.org/rfc/rfc6265#section-5.1.3