Plugin/BIND - extend the syntax to allow multiple addresses (#1512)

* Extend bind to allow multiple addresses. UTs added. Changes the log for server starting, adding address when available

* update readme for bind

* fixes after review

* minor fix on readme

* accept multiple BIND directives in blocserver, consolidate the addresses

* fixes after review - format logging server address, variable names

plugin/bind/README.md

@@ -6,23 +6,46 @@
 
 ## Description
 
-Normally, the listener binds to the wildcard host. However, you may force the listener to bind to
-another IP instead. This directive accepts only an address, not a port.
+Normally, the listener binds to the wildcard host. However, you may want the listener to bind to
+another IP instead.      
+
+If several addresses are provided, a listener will be open on each of the IP provided.
+
+Each address has to be an IP of one of the interfaces of the host.
 
 ## Syntax
 
 ~~~ txt
-bind ADDRESS
+bind ADDRESS  ...
 ~~~
 
-**ADDRESS** is the IP address to bind to.
+**ADDRESS** is an IP address to bind to.
+When several addresses are provided a listener will be opened on each of the addresses.
 
 ## Examples
 
 To make your socket accessible only to that machine, bind to IP 127.0.0.1 (localhost):
 
-~~~
+~~~ corefile
 . {
     bind 127.0.0.1
 }
 ~~~
+
+To allow processing DNS requests only local host on both IPv4 and IPv6 stacks, use the syntax:
+
+~~~ corefile
+. {
+    bind 127.0.0.1 ::1
+}
+~~~
+
+If the configuration comes up with several *bind* directives, all addresses are consolidated together:
+The following sample is equivalent to the preceding:
+ 
+~~~ corefile
+. {
+    bind 127.0.0.1 
+    bind ::1
+}
+~~~