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I am on double NAT (behind 2 routers).

I known how to get the public IP by visiting some webpages or use dig command. Yes I known WAN IP usually same as the public IP. I talk about WAN IP #2 that can be a private IP. I tried tracert and pathping commands but didn't work. Maybe we can't known the WAN IP by general way. But I saw one IP camera app can find it. Maybe it's "tinyCam Monitor" on android.

Boontawee Home
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    Hi @Boontawee Home. the question would benefit from additional clarifications. For example, you said I known how to get the public IP by visiting some webpages what do you mean by that? What commands did you try? Additional clarifications may help us to analyze your problem more accuratly! –  Sep 22 '18 at 13:44
  • Pub IP or WAN IP #1 can easy check by many ways eg. whatismyip.com or use command dig. Maybe it can't know WAN IP by general way. – Boontawee Home Sep 22 '18 at 14:18
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    Possible duplicate of What's the shortest way to find my WAN IP address at the command line? –  Sep 22 '18 at 14:18
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    I think you'd need some client on that address space... or a STUN service running on the "internal" WAN – RubberStamp Sep 22 '18 at 14:19
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    Do you know any details about the first NAT router? Also, tracert and pathping are Windows commands. Is there a Linux host on LAN with private range 2? AFAIK, tracert uses UDP packets; you may try tcptraceroute for TCP packets or mtr for ICMP packets, in the case the NAT router treats them differently. Some routers also offer an UPnP interface to sidestap NATing; you could try that as well. – dirkt Sep 22 '18 at 16:03
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    There is no general way to find out the address WAN IP2. Why would you need that address? – RalfFriedl Sep 22 '18 at 18:17
  • I am learning about network and making some IP camera software. In some case user can't access on router #1 eg: ISP or their company.

    I would like to have a function to check that user is on double NAT or single NAT. To check WAN IP by visit some webpage eg: whatismyip.com is one of the solutions to compare the result.

    I think external IP (WAN IP) can access via uPnP enabled routers. I need to learn practical of UPnP/IGD. Hope someone can teach me the command line.

     – Boontawee Home Sep 23 '18 at 15:09
  • Update!... MiniUPnP can show external IP on uPnP enabled routers. – Boontawee Home Sep 23 '18 at 15:27
  • ...and if you have UPnP enabled on your gateway router you get what you deserve. – Chris Davies Sep 24 '18 at 08:54

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Private LAN clients can known external IP only when the router enabled uPnP

I had recheck the android app "tinyCam Monitor". She known the external IP when router is enabled uPnP feature.

So I check around internet and found MiniUPnP (http://miniupnp.free.fr/) command that can show the external IP via UPnP/IGD. I don't know much about UPnP/IGD.

Old routers notes

UPnP implementations are potentially subject to security breaches. Badly implemented or configured UPnP IGDs are vulnerable. Security researcher HD Moore did a good work to reveal vulnerabilities in existing implementations : Security Flaws in Universal Plug and Play (PDF). A common problem is to let SSDP or HTTP/SOAP ports open to the internet : they should be only reachable from the LAN.

Boontawee Home
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    To make this a useful answer, at least describe how you used MiniUPnP, what your particular router showed when using it, and what brand and model of router it is - things will likely work differently for other routers. – dirkt Sep 23 '18 at 16:18