Why I can't access these sites from South Korea?

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http://serverfault.com – titaninternet.co.uk htmldog.com socialistworker.co.uk thinkup.org pentasia.com These websites are hosted by Titan Internet in UK. I can't access these websites from South Korea. (I can access by using proxy servers in other countries.) Titan Internet said that they haven't blocked any IPs from South Korea. (And it seems not that administrator of these websites blocked, too.) Also, some websites hosted by Titan Internet are accessible from South Korea. For example, muse.mu thegreencarwebsite.co.uk wdon.com these websites are accessible. Why is this happening? I want to know where I s (HowTos)