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Following situation:

When I request an echo reply of my public IP from my local network I get an ICMP timeout; on the other hand, making an echo request on my public IP from a machine from the internet (connected via ssh) returns an echo reply.

How do I know my public IP? I went to www.whatismyip.net. My ISP has assigned me a dynamic IP address, which is shared one (I was told by my ISP).

My friends don't reproduce this behavior with their networks, which means they get an echo reply pinging their public IP.

When I call my ISP they tell me that I should subscribe for a business plan which costs US$10 monthly extra and they talk about a static IP, so I just hanged up the phone. Morons.

What causes that I don't get an echo reply? How can I fix this error? I'd appreciate any feedback.

EDIT: My router is a D-Link DI-624.

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  • Are any of your firewalls blocking ICMP requests?
    – Nathan Osman
    Commented Jul 18, 2010 at 17:33
  • No, my router is replying to ICMP requests from the WAN.
    – Kenny Meyer
    Commented Jul 18, 2010 at 18:03

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Why do you consider this to be a problem? Is there some functionality that is not working properly? The failure is probably because the ICMP echo request message from the inside network is NATed to the external IP of the router. The router then receives the ICMP echo request from its own address and doesn't bother forwarding the response back to you. Unless you have a need to ping the external interface of your router, you probably don't need to worry about this. If you need to test connectivity, either ping the internal interface, or ping the next-hop gateway on the external side at your ISP.

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This is probably because NAT of your router is not well implemented.
Many cheap router doesn't allow data coming from the lan to reach external public IP.

What's append ? Your private IP is nated to your public IP, then you reach your public IP with public IP as source (as private has been NATed). Then the reply has same source and destination and the router is not able to do NAT again to change the destination to your private IP.

Check with your friend, but they probably don't have the same router manufacturer as yours

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  • So, you are suggesting me to try again with another router? My router is a D-Link DI-624.
    – Kenny Meyer
    Commented Jul 18, 2010 at 18:05
  • Yes, try with one of your friend router is possible, it will probably work
    – radius
    Commented Jul 18, 2010 at 18:20

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