Take the 2-minute tour ×
Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

I'm not an IT guy, i'm just home user which know a bit about networking. I'm trying to learn how the connection (LAN) is built in outer side of my home LAN. Here's the diagram :

PC (IP:192.168.1.100)
   |
   | (wirelessly)
   |
cisco router WRT54G2 as gateway (192.168.1.1 / 192.168.71.19)
   |
   | (via copper straight cable)
   |
cable modem
   |
   | (via coaxial cable)
   |
Internet provider (ISP)
   |
   |
   |
i n t e r n e t 

The last 2 nodes above (isp and internet) is the WAN. From my PC i connect to the router and see the configuration (router administration page), i can see that the router got external-ip: 192.168.71.19 (255.255.255.0) and gateway: 192.168.71.1 (255.255.255.0). So Logically like this :

-------------------------------------
| 192.168.1.100 (192.168.1.0/24)    |
-------------------------------------
      | 
      |
-------------------------------------
| 192.168.1.1 //                    |
| 192.168.71.19 (192.168.71.0/24)   |
-------------------------------------
      |
      |
------------------
| 192.18.71.1    |
------------------
      |
      |
------------- 
|     X X   |
-------------
      |
      |
  internet

I'm trying to solve the 'XX'. It maybe a public IP or maybe another level of NAT before it reaches the public IP. I believe this XX is firewalled or forbidden by the ISP . I can't use traceroute, it will return nothing but '*'.

My big question, how is the structure inside the XX (logical network diagram) ? i mean at least the typical setup , not specific to my isp. i guess the cable modem should connect to other router/switch but the weird thing i tried in app like 'cisco packet tracer', i'm not allowed to connect that cable modem to any router/switch. Anyone know what type of physical device should it connected to ?

The main goal, it's just for fun that i'm learning this. I'm trying to create a simulation of node by node from my host until it reach the internet. i'm using network simulation app, in this case i'm using cisco packet tracer to create every element that possible to built connection start from my local LAN (home) to the internal structure inside ISP until it reach the internet. Right now i'm stuck at cable modem point, i have no clue how to built the rest of the structure.

share|improve this question
    
Just for clarification, the "outer LAN" is called the WAN (Wide Area Network), whereas LAN stands for "Local Area Network". You should also look into something called NAT (Network Address Translation). This may shed some light on what you are trying to understand. –  Atari911 Jul 13 '13 at 18:44
    
Look up CIDR on wikipedia. It will make clear how larger networks are broken down into smaller networks by use of subnet masks. Also, look up Private Network on wikipedia as well for what is reserved for private and what is used for public networks (ie, 192.168.x.x is a private range, so even if your cable modem has that address on its WAN, it is still a private address - this is not something your ISP should be doing). –  MaQleod Jul 13 '13 at 19:58
    
Thanks i already checked all those stuff. I reedit my question to enhance it. Pls have a look. Thanks –  andio Jul 14 '13 at 3:13
    
the * means that the router at that hop didn't respond to the probes (the host didn't respond with a TTL expired packet), so trace route skips to the next hop in its analysis. since the host is not responding to ICMP, it will be very hard to observe the network that router controls. since the hop is clearly in your provider's private network, there won't be any source of publicly available information on it, and its likely that its part of a dynamic construct that doesn't even really exist. –  Frank Thomas Jul 14 '13 at 6:52

1 Answer 1

It seems the missing component is NAT (Network Address Translation) 192.168.#.# is not routable across the internet.

If 192.168.71.19 is truly your IP you are already behind another NAT.

Try : http://whatismyip.com

Given a limited number of internet IP's, NAT allows every home to use 1 internet IP to provide many internal IP addresses.

NAT is also, partly, a security feature as no internet device can directly communicate with any devices behind the NAT on your network.

In terms of security, NAT is not a substitute for firewall or anything else those are still needed.

The way it works is the router keeps a lookup table in memory. 192.168.1.10 requested google.com so when google.com responds the response goes back to that computer. Now obviously it is not quite that simple since multiple users can use google at a time, but it is the basic concept. The lookup table keeps track of enough metrics to make sure each connection is correctly associated with the correct computer.

The "*" means the node is not publicly identifiable. Typically a router inside of a company. If every device was exposed a hacker could use that information against said company.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.