Networking question

[anonymous51]

Hey guys I have a question this might be newbie but when we go on the internet I am wondering what is the public ip address that we are assigned by out ISP do? Because I've seen crime shows where they can say this address points to an internet cafe, hospital etc. I look forward to hearing from you thanks Gabe.

 

[freakdiablo]

An IP address is like a street address for your home. In really simplified terms, when you go to a website, download a file, whatever, the internet server looks at your IP and says "OK, I need to send the data *here*", in the same sense if someone wanted to mail you a physical letter they would need your home address.

Edit: To link it back to your comment about crime shows, in many cases there's a log of which IP is assigned to what customer, in terms of an ISP, or which device, in terms of an internal network.

 

[anonymous51]

An IP address is like a street address for your home. In really simplified terms, when you go to a website, download a file, whatever, the internet server looks at your IP and says "OK, I need to send the data *here*", in the same sense if someone wanted to mail you a physical letter they would need your home address.

Edit: To link it back to your comment about crime shows, in many cases there's a log of which IP is assigned to what customer, in terms of an ISP, or which device, in terms of an internal network.

Thanks for your help, freakdiablo can I add you as a friend on here? I look forward to hearing from you thanks Gabe.

 

[freakdiablo]

Thanks for your help, freakdiablo can I add you as a friend on here? I look forward to hearing from you thanks Gabe.

Sorry just realized you replied. Sure? But I'm far from the most helpful person here, lol.

 

[anonymous51]

Sorry just realized you replied. Sure? But I'm far from the most helpful person here, lol.

No worries you have helped me a lot.

 

[wingman99]

When sharing a public IP address how does the packet know what PC to go to on the network?

 

[knoober]

When sharing a public IP address how does the packet know what PC to go to on the network?

That's what DHCP does: assigns an internal IP for every device on the network. Or did I misunderstand what you asked?

 

[wingman99]

That's what DHCP does: assigns an internal IP for every device on the network. Or did I misunderstand what you asked?

Yes you have a misunderstanding. I'm asking what designates the route of the packets to the PC from a shared public IP.

 

[Janus67]

Yes you have a misunderstanding. I'm asking what designates the route of the packets to the PC from a shared public IP.

https://cs.stanford.edu/people/eroberts/cs201/projects/2000-01/packet-monitoring/background.htm

Probably wayyy more than you are looking for, but basically packets are tagged in ways and routers contain a list of machines in their dns and DHCP list to know when something is supposed to be heading there.

 

[wingman99]

I looked at your link and if the source on the packet is the privet IP then how does the shared public IP packet know what privet IP to send to? Since the header does not carry both the privet IP and public IP at the same time.

 

[freakdiablo]

It's been a while since I've really dove into that level of networking but believe that the base router/gateway does most of that processing and keeps track of which internal IP is communicating with which external IP - so in reality only the data blocks are the same and the headers are rebuilt on both sides of the router, each containing their associated IPs.

Sorry if I'm also misunderstanding you.

Edit: sorry I might be, Janus already posted something similar

 

[wingman99]

So the router keeps track of the client privet IP with the destination public IP header through NAT? So the packet with public IP source and destination sees the router NAT looking for source and destination public IP to convert to privet IP address?

 

[freakdiablo]

I could be wrong but believe that's the jist of it - as far as the outside network is concerned it just sees one destiantion - your IP, your modem. It then falls more to your router to sort things internally based on NAT, port assignment, and other info contained in the packet header.

 

[Janus67]

That sounds right to me (from my loose understanding of networking)

 

[don256us]

Think of it as if you lived in a large apartment complex. You all basically have the same address. The apartment manager knows which apartment you live in within the complex. The mailman delivers mail to the apartment manager who then distributes the mail to the individual apartments. That's the way a router would work. There may be a router in your house giving addresses like 192.168.*.* or 10.*.*.*. Your ISP also has a router(s) that gives each customer an IP address. Think of that like the city that you live in.

So the mail goes to the mayor who knows where the apartment complex is and gives it to the manager who knows where you live and you get your mail. Then you give that mail to the actual person in your apartment that requested it. At each level, the system keeps track of the final destination and routes it in that direction. Like where the mailman reads the city that the address lists and gets it to the mayor. The Mayor reads the apartment complex name and gets it to the manager. The manager reads the apartment number and gets it to you. You read the name of the person in your apartment that it is addressed to. Routers are doing that. There are several means of record keeping like DNS and DHCP and routers even have their own tables to help keep things going.

This is how the ISP can say that certain traffic went to a particular customer. Since their routers and other edge based equipment has to route and/or inspect each packet, they know which customer's account that traffic went to. Your account has your street address so your ISP knows to which street address certain traffic goes to if they cross refernce their account information with the traffic that they passed.

 

[wingman99]

Where it is fogy for me the packet header contains only the sending external IP address and receiving external IP address and the NAT converts the internal IP address to the shared external IP address. So when the packet header comes back to the router from the shared external IP address how does the router know what client to send the shared IP header packet to since it is a shared external IP address? The only thing I can think of is the router looks for the server senders external IP address for the NAT table look up to send to the correct PC. Router can't work like the mail service there is NAT conversion to the header packet and the header packet only has two IP address at a time.

 

[knoober]

Maybe we are just over thinking it. Pretty sure it would be in the header from the initial packet sent from your machine. Your machine makes the request to speak to their server through the router which does its NAT business and strips out all the local info before sending the request out on the interwebs? Just guessing though. I'm sure I will look into it more someday, but for now I just accept that the internet == magic

 

[wingman99]

I have been trying to figure out how the router works and all explanations on the net only state the router knows where to send the incoming packets with know explanations how it works.

 

[habbajabba]

It's called "memory addressing' and you would need to know how the architecture of the device itself is built to explain something so simple.

 

[Bill_Bright]

You router keeps track of which node (device on your side of the router) is sending the request via PAT (port address translation).