I know that routers will drop ip packets with private destination ip.Then how to route between private networks?
If there is no solution to that,then how do private networks in a big corporation communicate with each other?
routers will drop ip packets with private destination ip
No. Only when they are configured that way - usually when they route into a public IP range area. Consumer routers may be preconfigured that way in their firmware.
how to route between private networks?
Set up the router with a working routing table and let it do its job.
Routing private destination IP addresses across public IP networks involves tunneling, most often encrypted tunneling (VPN). The local tunnel gateway wraps the actual IP packet in a transport packet that's addressed to the remote gateway. The transport packet is routed normally and on arrival at the remote gateway, the wrapper is removed and the actual packet restored.
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Actually i have three Questions in this regard
IP ADDRESS:- Does router and default gateway same? if same , then why router (internet IP) address is public and Gateway IP address is local (i mean why both are different)
MAC ADDRESS:- what is the difference between WAN MAC address and ROUTER MAC address and Default Gateway MAC address , why are they different?
Difference between Data packets and IP packets? are data packets travel from a host to a remote server present in some other country through submarine cables or through router to router by hop-by-hop transport?
I am a new learner , please don't get angry if i asked something silly
Router and gateway are essentially the same - a gateway provides access to remote subnets. The hardware for that is called router. Routers route between networks.
A default gateway is a gateway to provide access to all subnets that are not specifically configured. At a minimum, a host requires a default gateway to connect to the Internet.
IP addresses are configured on (logical) interfaces. A router usually requires at least two interfaces, each configured with an IP address from the connected subnet.
Likewise, a MAC address is required for a physical interface - specifically for the data link layer to work (OSI layer 2). It uniquely identifies interfaces within a network segment and is used by network switches for forwarding.
A data packet can be many things. An IP packet is a packet (also protocol data unit PDU) on the network layer (OSI layer 3). IP packets travel between hosts around the globe and transport user data (payload) between them.
User data is actually transported by an application-layer protocol (e.g. HTTP) that in turn uses a transport-layer protocol (e.g. TCP) between processes/applications. The transport layer uses the network layer (IPv4 or IPv6) which in turn uses the data link layer (e.g. Ethernet) which in turn uses the physical layer (physical interfaces and cables).
When I send a request to web-server from one of my computers connected to home wi-fi router - how the response packet finds its way back to my computer and not to the other?
All computers in my local network have only one public IP and different private Ips (starting with 192.168...) - but source address in outgoing IP packet will be that public IP, so the destination IP for response packet will be also that public IP.
Where is the information about private IP (like 192.168.2.101) stored?
Thanks to NAT, several private IP addresses can share single public IP.
In both TCP and UDP each packet contains a source IP and a source port (along with a destination IP and port). When a machine in private network sends request to public server, NAT device/router overwrites private source IP+source port in the request packet with the public IP of the router and some unique port, and stores original source IP+port pair and overwritten source port in Translation Table. Remote server responds to public IP of the router+overwritten port number, router does a search in Translation Table by overwritten port number, and put original private ip+port into response packet and sends it to private machine (to original IP+port). Image from Wikipedia:
(more detailed on Wikipedia)
So the answer is: Translation Table on router allows to distinguish computers in local network and deliver responses to correct local machines.
Let's say that I have a home network of 5 computers. They all share the same external IP address.
Suppose a machine that is outside the network sends a request (as a client) to one of the 5 computers (this computer will be the server) in this home network. It sends its message to the external IP address. Then, how does the router know to what computer in the home network the message has to be routed to?
Typically when you talk about NAT, there are two main “flavours” - Source NAT & Destination NAT. There is another function called “PAT” (or Port Address Translation).
Source NAT is utilised when all your 5 computers are trying to reach out to the public (Internet) network. At this point your 5 computers get MASQUARADED with your public IPv4 address.
Destination NAT is what you’re asking for. In this case, you must configure your router/firewall (device that holds your public address & maintains your public connection) to “REDIRECT” or “DNAT” all incoming packets destined to a specific application (or port). For instance, if you have an HTTP server running on your private network server with address 10.0.0.3, you simply instruct your router to send all (or selective) TCP packets that have been sent to the public IP on ports 80/443 & send those to 10.0.0.3.
In DNAT scenario you must explicitly instruct your router/firewall about every type of expected, incoming connection. Another example can be that same public address is been used for SMTP server and thus sending all TCP packets received on port 25 to be sent to local server 10.0.0.4 this time. And so on and so forth
That’s in short how it works.
Network Address Translation (NAT) allows a single device, such as a router, to act as an agent between the Internet (or public network) and a local network (or private network), which means that only a single unique IP address is required to represent an entire group of computers to anything outside their network.
ADDRESS TRANSLATION (NAT) OVERLOAD allows your 5 computers to communicate with your router. Each computer has unique private IP address.
When computer1 tries to communicate with website, it sends packet to router.
Router replace the private IP address (example: 192.168.1.1) with single public IP address (example: 205.65.45.100) but uses same source port number (for example Port 5000) which is used by computer. It won’t change the source port number. And Router maintains entry in NAT table.
The reply from the (web server) internet arrives at your public interface of your router.
The router accepts packet and check the destination port entry. With the help of the NAT table, your router understands that it belongs to computer1. Router changes single public IP address (example: 205.65.45.100) with your internal private address (example: 192.168.1.1) and your computer receives it.
This process is applicable for all 5 computers.
Above scenario is only applicable if your computers act as a client. If your computer acts as a server then the solution is “Port forwarding”.
Port forwarding is needed when a machine on the Internet needs to initiate a connection to a machine that's behind a firewall or NAT router.
Refer video for detail information.
https://www.youtube.com/watch?v=-K6jMYBfuIY
I am facing a very strange problem. I have a task to establish a TCP connection to a server who has a trusted IP. And I have to run the code in a host with private IP address. The trusted IP is 10.10.10.15, which is also a private IP. And the question arises that the IP address of my host and the trusted IP is not on the same network. To be specific, my IP address is 10.0.35.1/24. Please let me know if there is any solution to this problem
Presumably these subnets, i.e. 10.10.10.0/24 (?) and 10.0.35.0/24, are part of your local network. You will need a Layer 3 device to perform inter-VLAN routing.
This will be a router with Layer 3 VLAN interfaces, in the Cisco world they would be SVIs, that would be acting as the default gateway of the subnets in your network. What happens is all traffic that needs to go between two hosts between different networks, has to go through their default gateway and it will be routed to the destination network/VLAN.
As long as the network devices between the two clients are able to route packets between these networks, the hosts will be able to reach each other. In your code, you simply need to specify that these packets need to go to the private IP address of the other host.
I'm curious why a client(android or c# based program, etc) behind a private router(or gateway, anyway with a private ip such as 192.168.xx.xx) can get a response from a request to a http server.
I know that this works, but just want to know how.
Is the client which is getting back the response need port forwarding unless it's not using a public ip?
He doesn't need port forwarding.
This can work by using NAT or PAT (Network Address Translation or Port Address Translation) configured in the Router mostly configured by the ISP's in the edge router.
-EDIT (more explanation added):
The edge router has some public IP (mostly pool of IP's) configured to communicate in internet (public network).
When the request that comes from internal network with private IP it takes that and changes the source IP (private IP) to one of the public IP's that has configured, thus the request would look like is made by the router itself.
Mostly will attach also a port number and save it in a database table (local db in router) with the private IP of the device who originally made the request and will forward the request to the internet.
Then, when the response is received by public server in that router, it will map it by the port with the private IP that had saved it in local db earlier, so it will know to whom it belonged originally, and will forward that to the IP