Hi, If using a user-agent that prefer IPv6 such as the Squid proxy, a timeout may frequently occur on logback.qos.ch. It seems to me that the IPv6 site does not exist. References: - http://ready.chair6.net/?url=https://logback.qos.ch - http://ipv6-test.com/validate.php In addition, it seems that AAAA records may not be returned depending on DNS query timing. ``` $ date; dig +noall +answer @8.8.8.8 logback.qos.ch aaaa Thu Mar 30 22:34:03 DST 2017 logback.qos.ch. 279 IN CNAME yvo.qos.ch. yvo.qos.ch. 279 IN AAAA 2a02:121e:969:1:201:c0ff: fe1c:5f7c $ date; dig +noall +answer @8.8.8.8 logback.qos.ch aaaa Thu Mar 30 22:34:05 DST 2017 logback.qos.ch. 299 IN CNAME te.qos.ch. ``` Would you please investigate this? Regards, Takuma Tsutsumi