For example, for a machine with vmware installed, there are at least three IP addresses listed by ipconfig:
Wireless LAN adapter Wireless Network Connection 4: Connection-specific DNS Suffix . : gateway.2wire.net Link-local IPv6 Address . . . . . : fe80::2d6b:91f7:5bdd:7103%21 IPv4 Address. . . . . . . . . . . : 192.168.2.100 Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . : 192.168.2.1 Ethernet adapter VMware Network Adapter VMnet1: Connection-specific DNS Suffix . : Link-local IPv6 Address . . . . . : fe80::c53a:65e3:112:731%16 IPv4 Address. . . . . . . . . . . : 192.168.172.1 Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . : Ethernet adapter VMware Network Adapter VMnet8: Connection-specific DNS Suffix . : Link-local IPv6 Address . . . . . : fe80::2119:1d74:2a9e:2c25%17 IPv4 Address. . . . . . . . . . . : 192.168.79.1 Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . :In the above example, VMnet1 and VMnet8 are virtual interfaces created by vmware software.
The most reliable way is to use the route table. On windows, "route print" command gives us something like:
Network Destination Netmask Gateway Interface Metric
0.0.0.0 0.0.0.0 192.168.2.1 192.168.2.100 25
127.0.0.0 255.0.0.0 On-link 127.0.0.1 306
192.168.79.1 255.255.255.255 On-link 192.168.79.1 276
192.168.172.1 255.255.255.255 On-link 192.168.172.1 276
We can see the default route uses interface 192.168.2.100.
On linux, we can check the route table at /proc/net/route
Iface Destination Gateway Flags RefCnt Use Metric Mask MTU Window IRTT p3p1 0002A8C0 00000000 0001 0 0 1 00FFFFFF 0 0 0 vmnet8 0052A8C0 00000000 0001 0 0 0 00FFFFFF 0 0 0 vmnet1 002B10AC 00000000 0001 0 0 0 00FFFFFF 0 0 0 p3p1 00000000 0102A8C0 0003 0 0 0 00000000 0 0 0In this example, we can see the default route uses interface p3p1.
I created ParseRoute class for retrieving local IP address and default gateway information from route table. Code for parsing route table on Windows:
private void parseWindows()
{
try
{
Process pro = Runtime.getRuntime().exec("cmd.exe /c route print");
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(pro.getInputStream()));
String line;
while((line = bufferedReader.readLine())!=null)
{
line = line.trim();
String [] tokens = Tokenizer.parse(line, ' ', true , true);// line.split(" ");
if(tokens.length == 5 && tokens[0].equals("0.0.0.0"))
{
_gateway = tokens[2];
_ip = tokens[3];
return;
}
}
//pro.waitFor();
}
catch(IOException e)
{
System.err.println(e);
e.printStackTrace();
}
}
Code for parsing route table on linux:
private void parseLinux()
{
try
{
BufferedReader reader = new BufferedReader(new FileReader("/proc/net/route"));
String line;
while((line = reader.readLine())!=null)
{
line = line.trim();
String [] tokens = Tokenizer.parse(line, '\t', true , true);// line.split(" ");
if(tokens.length > 1 && tokens[1].equals("00000000"))
{
String gateway = tokens[2]; //0102A8C0
if(gateway.length() == 8)
{
String[] s4 = new String[4];
s4[3] = String.valueOf(Integer.parseInt(gateway.substring(0, 2), 16));
s4[2] = String.valueOf(Integer.parseInt(gateway.substring(2, 4), 16));
s4[1] = String.valueOf(Integer.parseInt(gateway.substring(4, 6), 16));
s4[0] = String.valueOf(Integer.parseInt(gateway.substring(6, 8), 16));
_gateway = s4[0] + "." + s4[1] + "." + s4[2] + "." + s4[3];
}
String iface = tokens[0];
NetworkInterface nif = NetworkInterface.getByName(iface);
Enumeration addrs = nif.getInetAddresses();
while(addrs.hasMoreElements())
{
Object obj = addrs.nextElement();
if(obj instanceof Inet4Address)
{
_ip = obj.toString();
if(_ip.startsWith("/")) _ip = _ip.substring(1);
return;
}
}
return;
}
}
reader.close();
}
catch(IOException e)
{
System.err.println(e);
e.printStackTrace();
}
}
Usage Example:
ParseRoute pr = ParseRoute.getInstance();
System.out.println( "Gateway: " + pr.getGateway() );
System.out.println( "IP: " + pr.getLocalIPAddress() );
You can download source code here. Or view the main class online: ParseRoute.java
Please feel free to contact support@ireasoning.com if you have any questions.
Tags: Local IP Address Route Table