I'd like to simulate how my router will allow an outside intruder into my LAN if they know my dynamic IP address. So for that purpose, let's say that I know my IP address to be abc.def.ghj.klm: 80. Typing that into my browser address bar doesn't retrieve anything at all.

Does that mean that my router is configured to block connections coming from the outside or am I doing something wrong?

  • That means port 80 isn't open to the outside. The router could still be using 443 for HTTPS, or 22 for SSH, or some stupid protocol like SOAP.
    – forest
    Commented Dec 13, 2017 at 12:04
  • I'll imediately testify that, Actually there are three IP under the IPv4 DefaultGateway, which one is the realy IP of my computer the first or the last one ? Commented Dec 13, 2017 at 12:06
  • @forest I've tried each IPs respectively and with each ports 22, 80, 443, 444, 445. Commented Dec 13, 2017 at 12:10
  • Well those were just examples. How about you port scan it? There are 65535 TCP ports and 65535 UDP ports.
    – forest
    Commented Dec 13, 2017 at 12:11

1 Answer 1


If you try to access the server behind a router from outside (i.e. internet) and this fails then this means that either the port is blocked from outside or simply not explicitly forwarded in case of a NAT router. But it could also mean that the server is currently down or that some problems inside the LAN make it temporarily unreachable. Or it could mean that the DNS does not resolve to the currently correct IP address.

If you instead attempt to access the server from inside the same LAN by its external IP address (or hostname resolving to external IP address) then it could also be that your router does not support access to the external IP address from inside. This is also called NAT loopback (or NAT hairpinning or NAT reflection) and is not supported by all routers.

  • Thanks for the valuable info, but I know for sure that the router is up and functioning properly there is nothing wrong with server as well, remember that this is test case and I'm testifying my home network against vulnerabililties. For the time being I'm performing the port scaning as @forest suggested with nmap , as soon as it finishes I'll dump results Commented Dec 13, 2017 at 12:19
  • @SonyaBlade: No part of your question shows how your network is setup, from where you are doing the tests and if your router is capable of NAT loopback or not. Which suggests that you were not aware that these factors are relevant at all when asking "...am I doing something wrong?". Commented Dec 13, 2017 at 12:50
  • You seem to be offended I did mean no harm at all, I have to commit that I'm totally neophyte and sorry for not being verbose, I forgot to mention that my router is home router and in my test case I'm an outsider who knows the IP of my home router. Well after this I assume that all the possibilites to connect from the inside is eliminated, right? By the way, nmap UDP scan revealed that Discovered open port 123/udp but not finished yet so how am I supposed to interpret that? Commented Dec 13, 2017 at 13:27
  • @SonyaBlade: I've understood your comment in that you think that my answer does not really answer your question. I've tried to explain in my comment that it actually answers what I see as your question (i.e. "...am I doing something wrong?"). Commented Dec 13, 2017 at 13:32
  • @SonyaBlade: "port 123/udp" - that's NTP. The router probably has this open since it synchronizes its time with external hosts. Commented Dec 13, 2017 at 13:36

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .