Calculating SLAAC IPv6 Address in Java

SLAAC

With IPv6 a host on a network can use StateLess Address AutoConfiguration (SLAAC) to configure it’s network.

Routers will send out Router Advertisements telling the network which subnet is used in the network.

Based on their MAC address (modified EUI-64) a host will then obtain a IPv6 it will use.

Java

For the Apache CloudStack project I had to write Java code which would take a subnet and a MAC address as an argument and would generate a IPv6 SLAAC address from it.

Combining subnet 2001:db8:100::/64 with MAC address 06:7a:88:00:00:8b yields IPv6 address 2001:db8:100:0:47a:88ff:fe00:8b.

/*
 * Java code using Java-ipv6 from Google Code to convert
 * a given IPv6 subnet and a MAC address into a IPv6 address
 * calculated using SLAAC.
 *
 * Author: Wido den Hollander 
*/
import com.googlecode.ipv6.IPv6Address;
import com.googlecode.ipv6.IPv6Network;

public class IPv6EUI64 {
    public static IPv6Address EUI64Address(final IPv6Network cidr, final String macAddress) {
        if (cidr.getNetmask().asPrefixLength() > 64) {
            throw new IllegalArgumentException("IPv6 subnet " + cidr.toString() + " is not 64 bits or larger in size");
        }

        String mac[] = macAddress.toLowerCase().split(":");

        return IPv6Address.fromString(cidr.getFirst().toString() +
                Integer.toHexString(Integer.parseInt(mac[0], 16) ^ 2) +
                mac[1] + ":" + mac[2] + "ff:fe" + mac[3] +":" + mac[4] + mac[5]);
    }

    public static void main(String[] argv) {
        IPv6Network cidr = IPv6Network.fromString("2001:db8:100::/64");
        String mac = "06:7a:88:00:00:8b";
        IPv6Address eui64addr = EUI64Address(cidr, mac);

        /* This will print 2001:db8:100:0:47a:88ff:fe00:8b */
        System.out.println(eui64addr);
    }
}

The code can also be found on my Github Gist page.

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Wido den Hollander

I am the CTO at PCextreme B.V. and i will keep this blog just to post some interesting information about my daily work on Linux (and other) systems.