Thank you very much, guys. Definitively, IPv6 DNS resolution was the key for those sites. I've set a workaround based on dns_v4_first: http://www.squid-cache.org/Doc/config/dns_v4_first/ and things are working nice now. Greetings! -- View this message in context: http://squid-web-proxy-cache.1019090.n4.nabble.com/Strange-problem-with-some-sites-403-and-no-connection-tp4665328p4665741.html Sent from the Squid - Users mailing list archive at Nabble.com.