ESP8266.ping does not work as expected

The following is my output. It still does not work despite the fact that I'm connected to different router right now. Obviously there is bug somewhere, which is very discouraging

>var ESP8266=require("ESP8266");
=function () { [native code] }
>var Wifi = require("Wifi")
=function () { [native code] }
>Wifi.getIP();
={
  "ip": "192.168.2.203",
  "netmask": "255.255.255.0",
  "gw": "192.168.2.1",
  "mac": "5c:cf:7f:80:0c:86"
 }
>ESP8266.setLog(2);
=undefined
> 60000> Thu Jan 01 00:01:00 1970, heap: 10600
ESP8266.ping("192.168.2.1", function(e){ console.log(e);});
=undefined
>111956> Received a ping response!
{ "totalCount": 0, "totalBytes": 0, "totalTime": 0, "respTime": 0,
  "seqNo": 0, "timeoutCount": 0, "bytes": 0, "error": -1 }
>113081> Received a ping response!
{ "totalCount": 0, "totalBytes": 0, "totalTime": 0, "respTime": 0,
  "seqNo": 0, "timeoutCount": 0, "bytes": 0, "error": -1 }
>114256> Received a ping response!
{ "totalCount": 0, "totalBytes": 0, "totalTime": 0, "respTime": 0,
  "seqNo": 0, "timeoutCount": 0, "bytes": 0, "error": -1 }
>115406> Received a ping response!
{ "totalCount": 0, "totalBytes": 0, "totalTime": 0, "respTime": 0,
  "seqNo": 0, "timeoutCount": 0, "bytes": 0, "error": -1 }
>116531> Received a ping response!
116532> ping 5, timeout 5, total payload 0 bytes, 5703 ms 
{ "totalCount": 0, "totalBytes": 0, "totalTime": 0, "respTime": 0,
  "seqNo": 0, "timeoutCount": 0, "bytes": 0, "error": -1 }
>120000> Thu Jan 01 00:02:00 1970, heap: 10600