Inside IP address accessible from the internet

Unanswered Question
Aug 4th, 2008
User Badges:


I am having a very strange situation at a client site where i have recently installed a IP over Frame-relay for Internet Access for LAN users. the configuration of the IP/FR has been done on a cisco 805 series router. the weird thing is that i can access the internal ip address ( from the internet, which is the ip address of the serial.0 interface). As well the address which is the ISP side. I can do that at home and everywhere here in mauritius.

As far as i know private addresses cannot be seen on the internet, i want to know what might have caused this problem. I have attached the config of the cisco router 805. I need help

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
n.nandrekar Mon, 08/04/2008 - 23:45
User Badges:
  • Silver, 250 points or more


I dont think that is possible. What do you mean when you say "access" the internal ip? If you are just pinging, it is quiet possible that the ping is successful because some other host connected to the ISP is responding.

Sometimes the SP can allocate internal IP addresses to the home connections and NAT them to give access to the internet. I have seen a situation here in India, where I had a 3 DSL connections (within my room-mates) and the SP had allocated IPs in private range. We were able to ping each-other whough we had 3 seperate modems connecting to the SP.

So I would urge to verify whether its the same router/host that you are able to "access" by using telnet/ssh/capture on the host.

Also a word of caution to you : donot expose your sensitive config on forums. Mask any sensitive information like your public IP address etc.



(pls rate if helpful)

snahosany Tue, 08/05/2008 - 06:39
User Badges:

Hi Niranjan:

Thanks for your reply. I the ip address is the ip addres of my IP over frame relay router and i can both ping and telnet into the router using the ip

I would need your assistance for this matter.



n.nandrekar Tue, 08/05/2008 - 09:38
User Badges:
  • Silver, 250 points or more


Since the ip address is provided by the SP and is not strictly your internal ip address, there is possibility that it is reachable through the service provider network. If the SP is not explicitly blocking 1 customer to connect to another customer's assigned ip address, there is a possibility that this might happen. You would have to bear in mind though that you are still not on the internet. When you ping the ip from your home or internet cafe, you are still not routed to/through the internet if all have subscribed to the same SP. So I say that it would not be reachable from a different service provider. You are still pinging within your SP. The traffic is not going to the internet and that so you are able to reach.

This is my best guess!!! Else there is no explaination...

In the illustration attached, the custoners 1,2 and 3 are all given private IPs by the service provider and all can reach each other as they are internal to the SP. They dont traverse the internet.




This Discussion