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 开发者_运维知识库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

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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.

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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.

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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.