Windows knows when you have removed the network cable from your NIC. Is there a programmatic way to determine this via API in C++?
Note: I am not using .NET and this is for a closed LAN (not connected to Internet ever)
Raymond Chen blogged about something similar recently. Here is the relevant documentation. I think the MIB_IPADDR_DISCONNECTED flag is what you are looking for.
Use the Network List Manager api with the INetwork api.
You can register your app to receive callbacks when networks become connected/not connected.
Or you can get the list of networks and then check each of them to see if the machine is network connected or not
Remember that a windows machine will often have multiple networks set up (Ethernet, wifi, etc)
Remember that just because a network is connected, you may not have access to the internet. Eg you could have DNS or routing problems. Or you could be on a working network that is not connected to the internet.
Due to the above, many diagnostic tools also connect to a "known-good" internet server if they want to really know if they're connected or not. Something like google.com -- they spend a lot of money to make sure that their site is up all the time.
Finally, you can also have a semi-connected situation where packets are getting through but not enough to really enable communications to flow. To test this, don't just ping an internet site since that'd only be a pair of packets. Instead, open a TCP connection or something more than a ping.
Related
Currently in my chat p2p app, I need to open the port for other computers can connect to, but static ip is not allowed by the admin to open the port. Then I found a network programming exercise that seemed like a solution to this problem. The requirements are as follows:
"Write a program to test the UPnP protocol to
ADSL modem controller opens NAT gateway automatically.
In case you can not control the modem, find out and install a NAT Traversal technique to connect two clients in two NAT networks.
internet (use an intermediary server for primers
connect)."
Can anyone tell me what is an intermediate server for connection primitives?
Check https://www.noip.com/ :P. Maybe this can solve some of your problems ^^
You can simple setup DynDNS services. You will have one external domain name with any ip address.
But best way to setup SoftEther VPN solution. That can pass thought any NAT. You can keep your application server at the NAT subnetwork too. And that server will registered on common EtherVPN registry that allow connects from anywhere.
If you want smart solution embedded in your application. Please check similar solutions for VoIP communications. Like ICE, STUN, TURN. But that will not simple to implement.
I've been reading around on the www but just can't get the most important basics of P2P.
The diagram is like this:
[peer1]<-->[dsl-router1]<-->[central server]<-->[dsl-router2]<-->[peer2]
I'm developing a chat software on the central server. Chat messages being transfered thru' the central server well by now, however, I need to make the p2p file sharing feature because the bandwidth (the cable bandwith, not the transfer limit) of the server supposed for transfering chat messages only.
The problem is that, my software on central server knows the IPs and ports of router1 and router2, but not the peer1 and peer2 as these peers are behind the routers and don't have IP addresses.
How to actually transfer some data from peer1 to peer2 and vice versa without having this data passing thru' central server?
(and the worst case is that there is a wireless router between peer and dsl-router)
There are two basic ways of doing this. The new way is to use IGDP (opening a port via uPnP). This is described quite well here:
http://www.codeproject.com/Articles/13285/Using-UPnP-for-Programmatic-Port-Forwardings-and-N
If neither of the two nodes have a router supporting uPnP then another alternative is TCP hole punching, which is not perfect but works quite well in practice. This is described here:
http://www.brynosaurus.com/pub/net/p2pnat/
During some situations, "routers" supplied by the ISP may run on bridge mode, which directly exposes the peer computer on the internet (the computer gets a public internet address). If at least one side has this configuration (or in a similar situation that the peer client is not behind another device), then things should be rather straight forward: simply assign the central server's job to whoever that have this privilege.
In the other case where both peers only have a local address (e.g. 192.168.0.2) assigned to their computers, it would then be rather difficult to get through the routers; clients behind routers are for the most part unreachable from the outside unless they originated the request. Then, one solution to the problem is port forwarding. By doing port forwarding, either through explicitly written rules or UPnP, some ports on the peer computer is exposed to the public internet, as in the first situation where instead of only some ports the entire computer is exposed.
If you are without either of these, then there is no simple way to avoid sending through the central server. Though you could, potentially, find other peers who have the capability to transfer for others.
Let's say I have a server, and two clients connected to it. (via TCP, but it doesn't matter)
My goal is to allow a direct connection between those two clients. This is to allow direct voice contact between two players, for example, or any other client plugin they may have installed which don't need server interaction (like playing some kind of random game between the two). The server can be there to help setting up the connection.
From duskwuff's answer, I got several leads:
http://en.wikipedia.org/wiki/STUN which describes an algorithm to do that, and
http://en.wikipedia.org/wiki/UDP_hole_punching
From those, I got more leads:
http://www.h-online.com/security/features/How-Skype-Co-get-round-firewalls-747197.html
http://nutss.gforge.cis.cornell.edu/stunt.php -- A possible STUN implementation with TCP
With time, I could surely work out something for my program. For now I'm using C++ and TCP (Qt Sockets or Boost sockets), but if needed I don't mind doing UDP in C and wrapping it.
The bounty is there for any programmer having experience with those in C and C++ that may give tips to make this easier, by linking to example programs, updated libraries, or any other useful information. A documented, flexible & working C++ TCP implementation would be the best but I'll take what I get!
Punching TCP holes in NAT is sometimes/often possible (it depends of the NAT behavior). This is not a simple subject to learn, but read the corresponding chapter about NAT traversal from Practical JXTA II (available online on Scribd) to understand the nature of the issues to solve.
Then, read this. It comes from the guy who wrote that: http://nutss.gforge.cis.cornell.edu/stunt.php (one of the links in your question).
I am not a C/C++ specialist, but the issues to solve are not language specific. As long as you have access to TCP from your code base, that's enough. Keep in mind that implementing UDP traversal is easier than TCP.
Hope these tips help.
P.S.: I am not aware of a C/C++ implementation of the solution. The code mentioned in Cornell's link is NOT operational as confirmed by the author. I tried to resuscitate it myself, but he let me know it was completely tweaked for research purposes and far from production ready.
I'm not aware of any way to reliably punch through firewalls for TCP, but there's a similar method for UDP traffic that's pretty well documented:
http://en.wikipedia.org/wiki/STUN
http://en.wikipedia.org/wiki/UDP_hole_punching
A few links to projects that might be of interest or helpful:
http://sourceforge.net/projects/stun/
http://udt.sourceforge.net/
http://www.telehash.org/
You're looking for rendezvous server for NAT hole punching: the server that is publicly accessible (not behind NAT/firewall or they are properly configured) to help computers behind NAT/firewall to establish peer-to-peer connection.
UDP is more popular in NAT punching because provides much better results than TCP. Clear and informative description of UDP NAT hole punching can be found here.
If you need reliable communication, you can use reliable protocols over UDP:
SCTP (libraries) - standardized one, or
one of many custom protocols, e.g. RakNet (I used this library, it's quite mature and feature-rich and has NAT punching implementation), Enet or many others (Q8)
Ephemeral ports won't magically eliminate the need to relay through the server, because they are only valid during the life of the session opened through a well known service port. Basically ephemeral ports depend on a server session.
You will need to use the server to relay communications between both clients, that is act as a proxy server. One option would be to setup a SSH tunnel through a SSH proxy server, with the added benefit of security.
Still this doesn't guarantee that the firewall won't block the connection. That depends on the firewall type and configuration. Most residential routers that act as firewalls, by default block all incoming connections. This is normally fine because most of the time the computers behind the firewall act only as clients, which initiate the connections to the outside. And this setup varies, because some restrict initiating connections only to well known service ports like HTTP, HTTPS, FTP, SFTP, SSH, etc., and if your proxy server uses a non-well-known-service port then the connection will be blocked.
But firewalls can be setup to block outgoing traffic also, this is most common in corporate networks, which don't even allow direct connections to web servers and route everything through proxy servers, in order to control resource usage.
You can also research on the use of UPnP to open ports dynamically.
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.
i have known that winpcap library enabled a person to obtain advanced information about installed devices...
given all the networking devices found in the computer, how will i know which one of this has an internet connection?!
thanks:)
You typically don't care about this. Normally you just ask the network stack to make a connection, and don't worry about details.
However, each "device" will have its own IP address. You can request the network stack to use this IP address when making a connection.
Now, to figure which devices have an intenet connection, iterate over all of them, obtain their IP address, and try to create a connection from that originating IP to a destination IP on the Internet. Typically you already know such a destination IP, e.g. your companies webserver.
GetAdaptersInfo() will give you a list of all network adapters installed in a form that you can then use in GetIfEntry(). This latter function will tell you the operational status of an adapter, so you can at least tell if the adapter is plugged into a live hub/switch/router.
If you are particularly interested in IP connectivity, you could look to see if a default gateway is configured for that interface. Don't forget you might have to support IPv6 as well as IP4 if you try this.
Correlating the network adapters found by GetAdaptersInfo() with those found by pcap_findalldevs() is left as an exercise for the reader. I don't remember the details but it was fairly obvious.