if i close firewall and web shield would be ok . Could anybody tell me why?
i think that you mistakenly assume that “web shield” = “internet firewall”.
They are not the same thing.
i think you might be also have a chinese-to-english confusion of terms here… “web” in avast’s context really means web and not the entire set of internet protocols as a whole.
From what i know, web shield usually scans only http traffic on tcp port 80. (sometimes does SSL scanning too, using the browser plugins).