A Reliable way to Identify a computer by its ip address - c++

I have a network of computers that they will connect to the a server with DHCP, so I don't know what Ip address a computer will get when I connects to the server. If 192.168.0.39 for example is connected to the server can I identify the real computer behinde this ip address? ( I can install an external application on each client in order to send some data to server for example mac address or so... )

If you are responsible for the DHCP server, you can configure it to hand out a specific IP to a specific MAC. Having done that, you can be reasonably confident of that mapping -- it is possible to spoof MACs, so if you are worried about security, you'll need a much more heavy duty approach. If this is a casual application where the risk of that is low, you configure your DHCP server to hand out IPs based on MACs and then make use of those mappings in your application.

You might not even need the IP address. On an Ethernet network, all communication from a computer, whether it's IPv4, IPv6, or even IPX will be labelled with a MAC address that's stable over time and unique per network card.

Related

Socket programming: How a socket client may discover server IP address inside LAN?

Scope:
OS: MACOS, Windows;
Language: C++Boost library;
Description:
LAN has N computers with MacOS and Windows operating systems, where N ≈ 10. The IP addresses of the computer are not static and assigned by the network. On one of these computers (machine S) a socket server application is running. And on another machine (machine C) a client socket application is running. This is not a static setup, and next time it might be different computers with different IP addresses.
Update:
a server machine -- is a slave. A client machine is a master. A user can install client software in any computer in LAN, and server software in any other computer in LAN. Server take responsibility for the calculations which takes a lot of resources and just send a result to a client. So, the main idea is: a user of a master computer should not provide a server IP address, but the client soft should be able to discover it by itself.
Task: Client socket application does not know Server application IP address, and should be able to discover it.
Solution should be a cross-platform one (Boost C++)
Please suggest the best practices.
My best guess was: retrieve all the IP addresses of connected devices and socket->send_async_to them. And if I get answer in handle_receive callback -- this is a server app. But I did not find a way how to get all the IP addresses of LAN devices.
Thank you in advance for your suggestions and ideas.
use UDP to send request to all the computers in the network.Write a thread in server to respond udp request. then you can get response from the server and get the socket ip.

iOS NAT64 IPv6 environment issue

Now that apple has changed their review environment to an IPv6 only network ive been running into troubles with my application while testing.
The application requires the user to input their server/systems IP address, port (4401) and credentials to gain access to the application. Following the guidelines provided by apple i set up a NAT64 environment to test my application's compatibility. Running iOS 9.3.2 on an iphone 5s.
My work environment has several internal networks. I connected my iMac to the internal server (10.10.50.XX) via Ethernet which also has an external IP which is what i provide to apple. The 50 network does not run behind a proxy, but there are some sites which get filtered, but can access by confirming. I then shared my Ethernet connection through WiFI.
I connected the device and had internet access with the same pages being filtered. The device gets assigned a local-link address of 169.254.XX.XX. From what ive read my device is connecting to the ipv6 only network correctly, as the iphone does not show the ipv6 address only local link.
If I am correctly connected to the shared IPv6 network, the problem I am having is connecting to my server on the 50 network from my application. The application fails when ever i try to connected to the 10.10.50.XX network or the external(understandable because my imac is on the 50 internal network) .
Testing the application using IPv4 with a wireless router that is connected to the 50 network runs perfectly.I think it is an issue with the local link address not being able to see the 50 network or something.
Heres some brief background info on how i connect to the server. The user inputs all the credentials and the IP address and port of the server they want to connect to. The application saves this as a text (utf-8) and uses boost shared_ptr to send it to the cpp connection class which validates the credentials and provides access to the user. This cpp connection class handles the connection, synchronization, logging, requests and response from the server.
Is it possible to somehow get access to the 50 network, using the NAT64 internet sharing option?
If you're passing an IP address straight down to your network lib, then no. When your device is on the IPv6-only side of the NAT64, the server's IPv4 address is useless.
You almost certainly need a DNS name for the server you're trying to reach. The NAT64 relies first on DNS64 to create IPv6 addresses for your application when the server is IPv4-only. These synthesised addresses contain the IPv4 address(es) for the server, giving the NAT64 the information it needs to translate from IPv6 to IPv4.
Updating this to add: as suggested by user102008 in the comment thread attached to this answer, you may also be able to pass the IPv4 string literal though getaddrinfo() (see code listing 10-1 on this page). When you're behind a NAT64, a synthesised IPv6 address should be among the results returned by that call. The NAT64 will translate from this address back to IPv4 to reach the host you specified. In this case, if the system knows the correct prefix to use for the NAT64, a hostname is not necessary.

how to get IP address of a computers that is directly connected to my PC

I'm trying to write a function that can get me the IP adress (and the name of the device as bonus) of devices that are in my network, the network is gonna be a direct connection between two computers using Ethernet cable or creating an access point (using wi-fi)
I tried to search about how to do it but it seems like I need to listen to the network or something which seems to be difficult.
hope you can guide me to what I should do or read to get started.
Note: I'm using Windows on both computers.
Edited:
P.S: I need the IP Address so I can send a message to the other computer using winsock in a Client/Server program I wrote.
can't I make the server send its IP to the client or the opposite ?
If your software is running on both machines, you can have one (or both) machines send out a particular broadcast (or, if you prefer, multicast) UDP packet on a specific port. Your program should also be listening on that same port. When it receives that packet (using recvfrom()), recvfrom()'s fifth argument will contain the IP address of the machine that sent the packet, i.e. the IP address you want.
(If OTOH your software is not running on the remote machine, you'll need to use some more general-purpose discovery mechanism such as mDNS or LLDP -- hopefully you won't have to do that, though, as it's a good deal more complicated)

Qt5 Bind TCP Socket on Multihomed Network

I am having troubling using the new bind feature of the QTcpSocket class in Qt5. Any help figuring this out would be appreciated.
I have a multihomed server that contains two NICs each with a separate IP address. I have setup routing on the servers so that sending from the source address is sent out of the appropriate NIC regardless of the target remote address. That is, sending from x.x.x.0 goes out over eth0 and x.x.x.1 goes out over eth1 regardless of who the data is being sent to. These NICs are connected via ethernet to long range Wifi links that are then connected to a switch. These wifi links act as a transparent bridge and can rather be seen as two ethernet cables (but they are limited in bandwidth). The switch is then connected to a computer. The goal is to transfer data between the server and the computer, and to use the two wifi links in parallel to increase bandwidth. Although the server is physically a server, the software has the computer running as the software server (as others connect to it). That is, the physical server (software client) opens TCP sockets and attempts to connect to the listening computer (software server).
I use the bind feature of Qt5 to bind one TCP socket to the eth0 IP address and bind another TCP socket to the eth1 IP address. I have verified this works with other programs like PING or file transfer via SCP. See http://qt-project.org/doc/qt-5.0/qtnetwork/qabstractsocket.html#bind
When I call bind the call succeeds and subsequent requests for the local IP address returns the correct value. E.g. socket->bind(ip) returns true and then socket->localAddress() equals ip. However, when I call connectToHost the localAddress is lost when it starts the connection attempt and after connecting it has a different localAddress that is not the one I wanted it to have.
Can anyone shed light into what is going on? I am trying to avoid rewriting the software to reverse the roles of software client / server as these programs are quite big. Thanks for the help.
There is an open bug on this in the Qt project bug tracker.

C/C++ detect network type

I need to write a win32 c/c++ application which will be able to determine whether the PC it's running on is connected to one of 2 networks. The first network is the company LAN (which has no internet connection) and the second network is a standalone switch with a single PC connected to it (the PC that the program is running on).
I'm pretty new to network programming but so far I have tried testing to see if a network drive which is held on our LAN can be mapped. This works fine if the PC is connected to the LAN, the drive mapping succeeds so so LAN detection is successful. However, if the PC is connected to the switch, this results in a VERY long timeout which is not a suitable as it will delay the program so much as to make it unusable.
Does anyone have any alternative suggestions?
I'm using c/c++ in VS 6.0
[Update]
Whilst trying a few different ideas and looking at some of the suggestions below I thought I should update with some additional information as many (if not all) of the suggestions I don't think will work.
(1) The aforementioned LAN has no external connections at all, it is completely isolated so no resolving of external DNS or pinging websites is possible.
(2) Hostname, MAC address, IP, Default Gateway, Subnet etc etc (basically everything you see in ipconfig -all) are all manually configured (not dynamic from the router) so checking any of these settings will return the same whether connected to the LAN or the switch.
(3) Due to point (2), any attempts to communicate with the switch seem to be unsuccessful, in fact almost all networking commands (ping, arp etc) seem to fail - I think due to the machine trying to connect to the LAN when it isn't there :-(
One thing I have found which works is pinging the default gateway IP which times out when connected to the switch. This is sort of ok as I can reduce the timeout of ping so it doesn't just hang for ages but it feels like a bit of a hack and I would certainly appreciate any better solutions.
Thanks
As far as TCP/IP is concerned there is no such thing as a LAN on WAN. There are a set of non-internet routable addresses like 192.168.x.x and 10.x.x.x but these are sometimes used by ISP short of IP addresses.
You best bet is to use Asynchronous APIs when making TCP/IP connections. WIN32 defines a whole buch of OVERLAPPED APIs for this purpose. This will prevent your application from grinding to a halt while waiting for a remote connection.
Alternatively put the socket stuff into another thread and then only notify the UI when the operation is done.
I would first try to differentiate between the two using information available locally--that is, from your computer. Does the output of ipconfig /all differ depending on which network you're connected to? If so, exploit that difference if you can.
Is it possible to get the MAC address of the standalone switch? Of the switch that controls the company LAN? That would be a sure way to tell. Unless somebody cloned the MAC address.
If you try using the existence or non-existence of some network service to determine which network you're connected to, you can never be sure. For example, if you failed to map that network drive, all you know is that the network drive isn't available. You can't say for certain that you're not connected to the company LAN. Same is true if you use ping. Lack of response from a particular machine means only that the machine didn't respond.
Various things you can look at for differentiation:
DNS domain name (GetComputerNameEx)
MAC address of gateway (ping it, then GetIpNetTable)
Routing table(do you have a gateway and default route on the company LAN)
WNet discovered network resources (WNetOpenEnum, WNetEnumResource)
Ability to resolve external hostnames (try a 5-10 names like www.google.com, www.microsoft.com and so on, if one resolves you should have internet)
You'll have to decide how many indicators are "enough" to decide you're on one or the other LAN though if tests fail. Then keep retrying until you have a definite result.
http://msdn.microsoft.com/en-us/library/aa366071%28v=VS.85%29.aspx has a lot of network related functions that you can experiment with to create further indicators.