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I have Ubuntu 14.04 installed and I recently installed the same version from the same CD on my friend's computer. When I try to ping him I don't get any response, when I press Ctrl C to terminate ping it says it sent some number of packets, but none of them were received, 100% packet loss. I thought he might have a firewall installed, but that's unlikely because I just installed his Ubuntu. I read iptables comes with Ubuntu, but if so, why can he ping me and I can't ping him?

The two computers are not connected to a shared network, I'd like to ping him just like I can ping www.google.com.

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  • Whats his ip address and what is the ping command you are using?
    – Dan
    Aug 4, 2014 at 21:42
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    We need more information. How are the two computers connected? Are they on the same network? Is it through via wired or wireless connections? What exactly do you type to ping in the two computers? Do you type their local IP addresses? Do you type their names? Please edit your original question above with new information.
    – user68186
    Aug 4, 2014 at 21:42
  • @user68186 Edited.
    – shoham
    Aug 4, 2014 at 21:55
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    You're probably pinging his router, and he is pinging yours. Not necessarily a Ubuntu problem.
    – Jos
    Aug 4, 2014 at 21:58
  • @Jos Ubuntu is my (and his too) operating system, where else would this go? Is there a stackexchange for networking?
    – shoham
    Aug 4, 2014 at 22:37

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A very good way of troubleshooting why pings don't work can be done using traceroute:

traceroute -n <IPaddress>

If it is not installed, you can install it using sudo apt-get install traceroute.

From your comments on the question, you ran traceroute and it stopped at a certain IP address and displayed * * * asterisks afterwards, something like this:

traceroute to <IPaddress>, 30 hops max, 60 byte packets
 1  1.1.1.1  75.415 ms  75.348 ms  75.298 ms
 2  2.2.2.2  28.026 ms  28.025 ms  30.207 ms
 3  3.3.3.3  40.006 ms  39.999 ms  45.287 ms
 4  4.4.4.4  118.244 ms  90.393 ms  90.350 ms
 5  * * *
 6  * * *
 7  * * *
 8  * * *

This means that the traceroute got blocked and did not reach the destination. The network device 4.4.4.4 (or the device after it) is the device that is blocking the connection. Since you're going over the internet, I assume that these devices are not controlled by you. This means that you will not be able to ping your friend's IP because something on the internet is blocking it. He can ping you because there's nothing blocking pings originating from his network (that can also include the 4.4.4.4 device that is blocking your pings).

You can double check this by trying to ping his IP address from a different device, a device that is in a different LAN network than you, to verify that probably no one can ping his IP address (and that his ISP is probably blocking it).

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  • So I can't ping him because some router along the way has a decent firewall? That's weird... Can I make a detour around that router or something like that? Also, I asked another friend of mine to try to ping him, he couldn't either, him and me are on the same ISP while the friend we are trying to ping is on another ISP.
    – shoham
    Aug 4, 2014 at 23:48
  • Yes, a router along the way has a firewall that's blocking it. It's not weird at all man =), ISPs (or networks along the way) can block it. You can't make a detour around that router because you'll need access to the routing table of one of the routers along the way before you hit the firewall and edit them to go somewhere else. Since you and your third friend are on the same ISP, we still can't say for sure which "side" of the network is blocking it (your or the destination's ISP).
    – Alaa Ali
    Aug 4, 2014 at 23:53
  • Scratch that. Since you saw 14 IP addresses in your traceroute, it's probably not your ISP that's blocking it, but the destination's, or something along the way. To have some fun, ask your third friend to run a traceroute too (it can be run on Windows using tracert -d <IP>. Windows will probably give you different results; it can go further or even get blocked earlier because Windows uses a different traceroute way). Check if both your traceroutes stop at the same device. Remove the -n option (or -d in Windows) in the traceroute command to actually see what the IP addresses resolve to.
    – Alaa Ali
    Aug 4, 2014 at 23:55
  • I asked him. In the meanwhile, I'm curious, are those routers I'm routing through my ISP's and his ISP's only? Or are they also routers of other customers of the ISP? I mean, could it be that if I block port 80 on my firewall and someone in my ISP tries to log in to www.google.com, and I happen to be the shortest route to Google servers, could I deny him the connection? If so... that's just really dumb.
    – shoham
    Aug 5, 2014 at 0:34
  • No. The routers along the way are not just your ISP's and his, but probably other ISPs, depending on where you and him are located. Those are called the internet backbone routers. Read more about the internet backbone here and here. The ISP will never use customers as "hops" because 1) we probably only have 1 connection to the ISP, so how would the traffic go through us; it'll end up going back the same way it came in, 2) our links are very slow, in comparison.
    – Alaa Ali
    Aug 5, 2014 at 0:42

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