The servers showed no problems, but users from Russia to Hong Kong were typing the URLs into their browsers and getting blank pages. The country has long maintained an extensive-but-scattershot web censorship system — but on Thursday, it began blocking not just the sites, but the basic mechanisms of the web itself. For an internet service provider looking for the quickest way to a given IP, Iran’s new routes seemed like an easy shortcut — and when they arrived at the blank page, browsers simply assumed the page was down.