networking - practical example for the architectur of the internet

06
2014-04
  • geek_ji

    I am relatively new to the field of computer networking. I am trying to understand the subject. I know that the question here might be outdated but I still need to understand "why",because I am just unable to put the pieces in place and get a complete picture of the thing.

    All discussion here is in respect to IP v4.

    some one please explain me how exactly does the entire scenario work .... i work for ABC where in to access the internet i have to use a proxy- proxy.ABC.com. And ABC has many branches all over the world. So how does it happen? I mean does ABC purchase IP addresses from some authority and give each IP to every single office it has around the world? I mean how is this architecture defined.

    Please bear with me. The questions might sound stupid, but I am really confused.

    • Answers
  • wolfo9999

    Here is the shortest answer that I can provide while still giving good information:

    The domain www.ABC.com points to an IP address 123.123.123.123 Your PC asks a local DNS resolver what the IP is. The DNS resolver tells your PC, and it sends packets that are pointed to that IP (123.123.123.123) Your ISP has a network node. It looks at the IP address and it says "I know where that needs to go!" and it sends it off. If it doesn't know where to send the packets, it relays them to a different node that does know. When the packets reach the destination, it is up to the local routers at that building to send it to the correct local IP (192.168.x.x).

    IP addresses are handed out by a regional authority, which gets its IP addresses from a global authority called IANA (ironically it is funded by the US Defense Dept).

    As comments have said, there is a dictionary's worth of information regarding this.


    • Related Question

    networking - I can get in, but I can't get out
  • Rob Wilkerson

    Like most technical folks, I suppose, I'm my family's primary source of tech support. I'm a developer--not a sysadmin--by trade and tonight I bumped into something I've never seen before. I'm hoping someone here has.

    In order to better help my Mom, I have her set up on a home network behind a Linksys router (WRT54G). She's got a Mac, so I have her router set up to forward SSH requests to her laptop's internal IP. I also have her router running DDNS through DynDns. Tonight she called to tell me that she can't access the Internet.

    Assuming it was one of the many simple, stupid problems most of us encounter with parents, I logged into the router admin remotely and took a look around. Everything looked normal. Then I SSH'd into her machine to check out her IP, DNS, etc. settings. Everything still looked fine. Then I noticed something weird. When SSH'd into her machine, I can't ping her router.

    In other words, I seem to be able to access her computer through her router, but not access her router from her computer. A traceroute dies immediately as well. Any ideas what I might try next? I've bounced her computer and even unplugged her router (it was plugged back in, of course).

    Thanks.

    UPDATE:

    Oddly, this could be a problem at the ISP level. I walked her through bypassing the router all together (plugging her computer directly into her cable modem) and she still can't get out (where "get out" means "access a web page using Safari"). What confuses me is that I'm able to get in. That seems very odd to me.


    • Related Answers
  • Helvick

    Clearly internal traffic is traversing the network fine and the NAT router part is working OK as you are getting in, and the return traffic is getting back. Your error is mistaking ping and tracert for tools that tell you whether something is up\available - they only tell you information about how the target responds to ICMP traffic.

    Ping\tracert use ICMP which may well be just being dropped by her router so if they don't respond that doesn't indicate that anything is broken. It all depends on how the router has been configured. My (home) router drops external ICMP traffic aimed at its external interface so I can (normally) ping the inner (private) address but not the outer (public) address. I can also disable ICMP totally on it and get no response on either side but its still working properly in all cases, I can manage it through it's normal web admin interface and it routes properly.

  • Matt Beckman

    Perform a route print in a command prompt to see if there is any funky routing:

    route print

    Post the output.

    Edit: Sorry, Mac. Open a terminal and type "route".

  • Mircea Vutcovici

    It looks that a firewall on your mom computer our router is filtering the traffic. You should run on your mom computer:

    arp -d <IP_router>
ping -c1 <IP_router>
arp -n <IP_router>

    If you see the arp entry with the IP and the MAC address of the router, then you have a issue with the firewall on her computer or on her router.

    If traceroute "dies" immediately this means that it has received an ICMP error message (as oposed to timeout). This confirms the firewall issue.