Index: src/resolver.cr
==================================================================
--- src/resolver.cr
+++ src/resolver.cr
@@ -98,24 +98,48 @@
       case used_ns.family
       when Socket::Family::INET6
         if @v6_sock.nil?
           @v6_sock = s = UDPSocket.new
           s.bind "::", 0
+          start_recv_loop(s)
         end
         sock = @v6_sock.not_nil!
       when Socket::Family::INET
         if @v4_sock.nil?
           @v4_sock = s = UDPSocket.new
           s.bind "0.0.0.0", 0
+          start_recv_loop(s)
         end
         sock = @v4_sock.not_nil!
       else
         raise ArgumentError.new("Nameserver must be INET or INET6")
       end
       sock.send(context.raw_data, used_ns)
     end
+
+    def start_recv_loop(sock : UDPSocket) : Nil
+      spawn do
+        buf = Bytes.new(0x10000)
+
+        until sock.closed?
+          begin
+            len, addr = sock.receive(buf)
+          rescue ex : IO::Error
+            p ex
+            break if sock.closed? && ex.os_error.nil?
+            raise ex
+          end
+          handle_packet(buf[0, len], addr)
+        end
+      end
+    end
+
+    def handle_packet(packet : Bytes, sender : Socket::IPAddress)
+      p packet
+    end
 
     def stop : Nil
-      # TODO
+      @v6_sock.try { |s| s.close }
+      @v4_sock.try { |s| s.close }
     end
   end
 end

Index: tests/example.cr
==================================================================
--- tests/example.cr
+++ tests/example.cr
@@ -6,5 +6,9 @@
 query = AsyncDNS::Query.new("crystal-lang.org", AsyncDNS::DNSClass::IN,
   AsyncDNS::RRType::A)
 
 resolver = AsyncDNS::Resolver.new
 resolver.resolve(query) { |response| p response }
+
+sleep 2
+resolver.stop
+sleep 2