Convert MacAddress to IPv6 Link Local in Java

Question

I need to convert a Mac Address into an IPv6 Link Local address. This link-local IPv6 is infered from the NIC’s mac address. The conversion procedure is as given below.

1. take the mac address: for example 52:74:f2:b1:a8:7f

2. throw ff:fe in the middle: 52:74:f2:ff:fe:b1:a8:7f

3. reformat to IPv6 notation 5274:f2ff:feb1:a87f

4. convert the first octet from hexadecimal to binary: 52 -> 01010010

5. invert the bit at index 6 (counting from 0): 01010010 -> 01010000

6. convert octet back to hexadecimal: 01010000 -> 50

7. replace first octet with newly calculated one: 5074:f2ff:feb1:a87f

8. prepend the link-local prefix: fe80::5074:f2ff:feb1:a87f

This seems to be a lot of specific string manipulation and conversion between number systems. I was looking for a utility class in Java which could help me do the same in a more efficient manner. I see that Java has methods in InetAddress to determine if the address in question is a link local.

Answer 1

The IPAddress Java library has methods to do this. Disclaimer: I am the project manager of that library.

Here is sample code using your example MAC address 52:74:f2:b1:a8:7f

   String str = "52:74:f2:b1:a8:7f";
   try {
      MACAddress mac = new MACAddressString(str).toAddress();
      IPv6Address linkLocal = mac.toLinkLocalIPv6();
      System.out.println("converted " + mac + " to IPv6 link local " + linkLocal);
   } catch(AddressStringException e) {
      // handle invalid address string here
   }

Output is:

converted 52:74:f2:b1:a8:7f to IPv6 link local fe80::5074:f2ff:feb1:a87f

More examples are in the wiki.