plugin/bind: Discard link-local addresses on binding by interface name (#4531)

* Discard link-local addresses on binding
Signed-off-by: Mohammad Yosefpor <myusefpur@gmail.com>

* Update plugin/bind: README.md
Signed-off-by: Mohammad Yosefpor <myusefpur@gmail.com>

* Except for IPv6 link-local only
Signed-off-by: Mohammad Yosefpor <myusefpur@gmail.com>

plugin/bind/README.md

@@ -13,7 +13,7 @@ If several addresses are provided, a listener will be open on each of the IP pro
 
 Each address has to be an IP or name of one of the interfaces of the host. Bind by interface name, binds to the IPs on that interface at the time of startup or reload (reload will happen with a SIGHUP or if the config file changes).
 
-If the given argument is an interface name, and that interface has serveral IP addresses, CoreDNS will listen on all of the interface IP addresses (including IPv4 and IPv6).
+If the given argument is an interface name, and that interface has serveral IP addresses, CoreDNS will listen on all of the interface IP addresses (including IPv4 and IPv6), except for IPv6 link-local addresses on that interface.
 
 ## Syntax
 

plugin/bind/setup.go

@@ -37,7 +37,9 @@ func setup(c *caddy.Controller) error {
 					}
 					for _, addr := range addrs {
 						if ipnet, ok := addr.(*net.IPNet); ok {
-							all = append(all, ipnet.IP.String())
+							if ipnet.IP.To4() != nil || (!ipnet.IP.IsLinkLocalMulticast() && !ipnet.IP.IsLinkLocalUnicast()) {
+								all = append(all, ipnet.IP.String())
+							}
 						}
 					}
 				}