How can I make sure the system is connected via LAN?
In my Swing application (with web launch) I need to manually enter the IP addresses of the computers that I want to grant access to the application, now during the enetring of IP addresses I want to check that the machine IP address I entered is connected to my machine (acting as a local server) only via LAN (via a switch, not in the case of a router) or not. Because if the machine is not on the local network, it should not give permission to access the application.
How can I achieve this?
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As far as I understand your problem, you need to check if a specific IP is included in your application on a direct connect network for the client host.
If this is the case, then using simple ping will not work for you, since ping will turn on packet routing. Therefore, even the hosts behind the routers will answer.
As a workaround, you can add the "-t 1" option to ping, which specifies the TTL for ICMP packets so that they cannot pass through the router.
Or look at the following sample if you want something like this to be implemented in java (you should take it for your needs):
public class IsAddressDirectlyConnected {
private static class Network {
int network;
int mask;
Network(int n, int m) {
network = n;
mask = m;
}
};
// list of networks on interfaces of machine this code is being run on
List<Network> mDirectlyAttachedNetworks = new ArrayList<Network>();
private int addrBytesToInt(byte[] addr) {
int addri = 0;
for (int i = 0; i < addr.length; ++i)
addri = (addri << 8) | ((int)addr[i] & 0xFF);
return addri;
}
private void collectLocalAddresses() {
try {
Enumeration<NetworkInterface> nifs = NetworkInterface.getNetworkInterfaces();
while (nifs.hasMoreElements()) {
NetworkInterface nif = nifs.nextElement();
if (nif.isUp()) {
List<InterfaceAddress> ias = nif.getInterfaceAddresses();
for (InterfaceAddress ia : ias) {
InetAddress ina = ia.getAddress();
if (ina instanceof Inet4Address) {
int addri = addrBytesToInt(ina.getAddress());
int mask = -1 << (32 - ia.getNetworkPrefixLength());
addri &= mask;
mDirectlyAttachedNetworks.add(new Network(addri, mask));
}
}
}
}
} catch (SocketException ex) {
System.err.println("Socket i/o error: " + ex.getLocalizedMessage());
}
}
public boolean isDirectlyAttachedAndReachable(InetAddress address) {
int checkedAddr = addrBytesToInt(address.getAddress());
try {
if (!address.isReachable(1000))
return false;
} catch (IOException ex) {
System.err.println("Failed to check reachability: " + ex.getLocalizedMessage());
return false;
}
for (Network n : mDirectlyAttachedNetworks) {
if ((checkedAddr & n.mask) == n.network)
return true;
}
return false;
}
public IsAddressDirectlyConnected() {
collectLocalAddresses();
}
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
IsAddressDirectlyConnected iadc = new IsAddressDirectlyConnected();
if (args.length == 1) {
try {
boolean check = iadc.isDirectlyAttachedAndReachable(Inet4Address.getByName(args[0]));
System.out.println("Given IP is " + (check ? "" : "not ") + "on directly attached network " + (check ? "and " : "or not ") + "reachable from local host.");
} catch (UnknownHostException ex) {
System.err.println("Failed to parse address: " + ex.getLocalizedMessage());
}
} else System.out.println("Specify address to check.");
}
}
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