Add an option to disable IPv6, this option is available to client only

doh-client/doh-client.conf

@@ -65,5 +65,13 @@ no_cookies = false
 # the same configuration as most public DNS servers.
 no_ecs = false
 
+# Disable IPv6 when querying upstream
+#
+# Only enable this if you really have trouble connecting.
+# Doh-client uses both IPv4 and IPv6 by default and should not have problems
+# with an IPv4-only environment.
+# Note that DNS listening and bootstrapping is not controlled by this option.
+no_ipv6 = false
+
 # Enable logging
 verbose = false