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I tried to ping a D-link router 110.90.xxx.xxx, but I get:

Request timed out

I'm sure the router was online, and router firewall function was not turned on. What can cause this to happen?

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Isn't 110.x.x.x in the public range? Also, what model is this router? –  ekaj Mar 4 '13 at 20:56
    
And what's with the firewall on the computer you're pinging from? Anyways, I can successfully ping my own D-Link router using its either private or public IP address. –  Desmond Hume Mar 4 '13 at 20:57
    
Is the router actually paying attention to ICMP? Can you ping it from other machines? What IP address does your computer have? –  MaQleod Mar 4 '13 at 20:58
    
yes, 110.x.x.x is in the public range, I'm not trying to ping the router from my local network. I'm trying to ping a remote computer. model is DI-5 –  user22105 Mar 4 '13 at 20:59
    
@MaQleod He clearly doesn't feel like disclosing his IP address =) –  Desmond Hume Mar 4 '13 at 20:59

1 Answer 1

Two Types of Ping

There are two types of ping:

  • ICMP (Internet Control Message Protocol)
  • UDP (User Datagram Protocol)

Even if your firewall is "off", the default behavior might be to silently ignore pings.

Pings are necessarily round trip: in order to time anything, you must know how long it took for the endpoint to receive your packet. In order to know that, the endpoint has to send something back to you. So any ping, whether ICMP or UDP, has to involve two steps:

Your client sends a ping packet ----> router

Router sends back some kind of packet to your client, whether it's saying "oh hello there", or "that port is closed!", or "I don't understand the protocol you're speaking!" -----> your client

This "round trip" can be timed, but a one-way packet alone cannot be timed, because without a response, the client doesn't know how long it took, or if it ever even got there in the first place.

So if the default behavior of the router is to silently ignore pings on closed ports (which is a sensible behavior even if the firewall is off), the request will always time out.

Things you can try:

  • See if the router has an explicit option to enable ping
  • If you're using a ping client that uses UDP, try ICMP instead
  • If you're using a ping client that uses ICMP, try UDP instead

I don't know whether your ping client uses ICMP or UDP because you did not specify any information at all about the nature of your client PC, whether it's Linux, Mac, Windows, BSD, or some custom OS you wrote yourself.

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does this also ignore say a magic packet(for WOL)? I initially tried to ping the IP. I got a timed out response. But then I tried to straight up send a magic packet to the router, but wasn't successful at waking up a computer(running Windows) behind that router. –  user22105 Mar 4 '13 at 21:12
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wol doesn't make it through NAT, at least not without some severe tweaking on the router, but even then, it is iffy. –  MaQleod Mar 4 '13 at 21:15
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As MaQleod said, the router won't automatically forward packets to a computer on its LAN/NAT unless you have specific forwarding rules set up, because the default behavior for an inbound packet hitting a router is to ignore it (unless it's ICMP, which might be allowed), unless there are exceptional rules which say to forward, or if there is an established connection (e.g. a TCP socket) which allows for bidirectional communication. –  allquixotic Mar 4 '13 at 21:19

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