6to4.ipv6.microsoft.com

Recently installed ZoneAlarm on my machine, and I'd like to understand a bit
more about some of the things it is doing, and this is one I'm not sure
about. The alert says "The firewall has blocked Internet access to
6to4.ipv6.microsoft.com (192.88.99.1) (IP Protocol 41) from your computer."
Is this something I should be worried about, or is it something I can
ignore, or is it even an access I should be allowing to happen, and if so
what is likely to be requesting the access?

TIA.




Fantrace