Understanding JDK 1.6 on Ubuntu Linux IPv6 output handling -

i'm running ubuntu 10.10 , hosts configuration following:

root@maxim-desktop:~# cat /etc/hosts 192.168.20.20   maxim-desktop   # added networkmanager 192.168.10.20   maxim-lp 127.0.0.1       localhost.localdomain   localhost ::1     maxim-desktop   localhost6.localdomain6 localhost6  # following lines desirable ipv6 capable hosts ::1     localhost ip6-localhost ip6-loopback fe00::0 ip6-localnet ff00::0 ip6-mcastprefix ff02::1 ip6-allnodes ff02::2 ip6-allrouters ff02::3 ip6-allhosts root@maxim-desktop:~# cat /etc/resolv.conf  # generated networkmanager nameserver 192.168.20.1 root@maxim-desktop:~# cat /etc/hostname  maxim-desktop root@maxim-desktop:~# hostname  maxim-desktop root@maxim-desktop:~#  hostname --fqdn root@maxim-desktop:~# ifconfig  eth0      link encap:ethernet  hwaddr 00:1c:c0:f2:ba:89             inet addr:192.168.20.20  bcast:192.168.0.255  mask:255.255.255.0           inet6 addr: fe80::21c:c0ff:fef2:ba89/64 scope:link           broadcast running multicast  mtu:1500  metric:1           rx packets:9023854 errors:0 dropped:0 overruns:0 frame:0           tx packets:8532803 errors:0 dropped:0 overruns:0 carrier:0           collisions:0 txqueuelen:1000            rx bytes:4839992361 (4.8 gb)  tx bytes:1067998152 (1.0 gb)           interrupt:20 memory:d3300000-d3320000   lo        link encap:local loopback             inet addr:127.0.0.1  mask:255.0.0.0           inet6 addr: ::1/128 scope:host           loopback running  mtu:16436  metric:1           rx packets:12333251 errors:0 dropped:0 overruns:0 frame:0           tx packets:12333251 errors:0 dropped:0 overruns:0 carrier:0           collisions:0 txqueuelen:0            rx bytes:3216352432 (3.2 gb)  tx bytes:3216352432 (3.2 gb) 

i'm trying reach same result within java code.

sadly, following code doesn't seem cut through.

//copyright (c) 2011, maxim veksler //all rights reserved. // //redistribution , use in source , binary forms, or without //modification, permitted provided following conditions met: //    * redistributions of source code must retain above copyright //      notice, list of conditions , following disclaimer. //    * redistributions in binary form must reproduce above copyright //      notice, list of conditions , following disclaimer in //      documentation and/or other materials provided distribution. //    * neither name of <organization> nor //      names of contributors may used endorse or promote products //      derived software without specific prior written permission. // //this software provided copyright holders , contributors "as is" , //any express or implied warranties, including, not limited to, implied //warranties of merchantability , fitness particular purpose //disclaimed. in no event shall <copyright holder> liable //direct, indirect, incidental, special, exemplary, or consequential damages //(including, not limited to, procurement of substitute goods or services; //loss of use, data, or profits; or business interruption) caused , //on theory of liability, whether in contract, strict liability, or tort //(including negligence or otherwise) arising in way out of use of //software, if advised of possibility of such damage.  import java.net.inet4address; import java.net.inet6address; import java.net.inetaddress; import java.net.networkinterface; import java.net.socketexception; import java.util.enumeration;  import org.slf4j.logger; import org.slf4j.loggerfactory;  /**  * hostname , ip address info, based on jdk6 networkinterface  *   * @author maxim veksler <maxim@vekslers.org>  */ public class networkutil {     private static logger log = loggerfactory.getlogger(networkutil.class);      public static void main(string[] args) {         system.out.println("mac: " + networkutil.getmachinemac());         system.out.println("hostname: " + networkutil.getmachinehostname());         system.out.println("ip: " + networkutil.getmachineipaddress());         system.out.println("hostname ipv6: " + networkutil.getmachineipv6hostname());         system.out.println("ip ipv6: " + networkutil.getmachineipv6address());     }      /**      * mac address of remote ip (if on local lan).       * @param hostnameorip target ip or hostname (if have dns configured).      *       * @return mac address if ip in local lan, null if not.      */     public static string getremotehostmac(string hostnameorip) {         try {             inetaddress address = inetaddress.getbyname(hostnameorip);             networkinterface networkinterface = networkinterface.getbyinetaddress(address);             return obtainmacfromaddress(networkinterface);         } catch (exception e) {             if(log.isdebugenabled()) {                 log.debug("failed obtain mac address address " + hostnameorip, e);             }         }          // means had failure.         return null;     }      /**      * machine address of machine running on.      * @return 08-00-27-dc-4a-9e or null if can't obtain mac      */     public static string getmachinemac() {         try {             return obtainmacfromaddress(getnonloopbacknetworkinterface());         } catch (exception e) {             if(log.isdebugenabled()) {                 log.debug("failed obtain mac address localhost", e);             }         }          return null;     }      /**      * machine hostname, based on ipv4 configurations.      *       * @return string representing fqdn or null if can't find hostname      */     public static string getmachinehostname() {         try {             networkinterface networkinterface = getnonloopbacknetworkinterface();             inet4address address = getinet4address(networkinterface);             if(address != null)                 return address.getcanonicalhostname();         } catch (exception e) {             if(log.isdebugenabled()) {                 log.debug("failed obtain machinehostname", e);             }         }          return null;     }      /**      * machine hostname, based on ipv6 configurations.      * @return string representing fqdn or null if can't find hostname      */     public static string getmachineipv6hostname() {         try {             networkinterface networkinterface = getnonloopbacknetworkinterface();             inet6address address = getinet6address(networkinterface);             if(address != null)                 return address.getcanonicalhostname();         } catch (exception e) {             if(log.isdebugenabled()) {                 log.debug("failed obtain ipv6hostname", e);             }         }          return null;     }       /**          * machine ip, based on ipv4 configurations.      *       * @return string representing ip or null if can't find configured interface      */     public static string getmachineipaddress() {         try {             networkinterface networkinterface = getnonloopbacknetworkinterface();             inet4address address = getinet4address(networkinterface);             if(address != null)                 return address.gethostaddress();         } catch (exception e) {             if(log.isdebugenabled()) {                 log.debug("failed obtain machineipaddress", e);             }         }          return null;     }      /**      * machine ip, based on  ipv6 configurations.      *       * @return string representing ip or null if can't find configured interface      */     public static string getmachineipv6address() {         try {             networkinterface networkinterface = getnonloopbacknetworkinterface();             inet6address address = getinet6address(networkinterface);             if(address != null)                 return address.gethostaddress();         } catch (exception e) {             if(log.isdebugenabled()) {                 log.debug("failed obtain machineipv6address", e);             }         }          return null;     }       /*      * ########################      * helper private functions      */      private static string obtainmacfromaddress(networkinterface networkinterface) throws socketexception {         if(networkinterface != null) {             byte[] mac = networkinterface.gethardwareaddress();             if(mac == null)                  throw new error("failed obtain mac address interface: " + networkinterface.getdisplayname());              stringbuilder stringbuilder = new stringbuilder(17);             /*              * extract each array of mac address , convert hexa              * following format 08-00-27-dc-4a-9e.              */             (int = 0; < mac.length; i++) {                 stringbuilder.append(string.format("%02x%s", mac[i], (i < mac.length - 1) ? "-" : ""));             }              return stringbuilder.tostring();         }          return null;     }      private static inet4address getinet4address(networkinterface networkinterface) {         if(networkinterface != null) {             enumeration<inetaddress> nicaddresses = networkinterface.getinetaddresses();             while(nicaddresses.hasmoreelements()) {                 inetaddress address = nicaddresses.nextelement();                  if(address instanceof inet4address)                     return (inet4address)address;             }         }          return null;     }      private static inet6address getinet6address(networkinterface networkinterface) {         if(networkinterface != null) {             enumeration<inetaddress> nicaddresses = networkinterface.getinetaddresses();             while(nicaddresses.hasmoreelements()) {                 inetaddress address = nicaddresses.nextelement();                  if(address instanceof inet6address)                     return (inet6address)address;             }         }          return null;     }      private static networkinterface getnonloopbacknetworkinterface() throws socketexception {         // need iterate on nic's machine has because stupid ubuntu not assign         // mac address default loopback interface...         enumeration<networkinterface> b = networkinterface.getnetworkinterfaces();         while(b.hasmoreelements()) {             networkinterface networkinterface = b.nextelement();             enumeration<inetaddress> inetaddresses = networkinterface.getinetaddresses();             while(inetaddresses.hasmoreelements()) {                 inetaddress address = inetaddresses.nextelement();                 if(!address.isloopbackaddress())                     return networkinterface;             }         }          // means haven't found non loopback interfaces. bummer, return empty handed.         return null;     }  } 

the following printed on machine:

mac: 00-1c-c0-f2-ba-89 hostname: maxim-desktop ip: 192.168.20.20 hostname ipv6: fe80:0:0:0:21c:c0ff:fef2:ba89%2 ip ipv6: fe80:0:0:0:21c:c0ff:fef2:ba89%2 

• as can see hostname output ipv4 & ipv6 not same, wonder why should this?
• also, meaning of %2 get's attached ipv6 related queries - bug in code or jvm / linux kernel issue?

thank you,
maxim.

1. if @ code, here's does:

   • find non-loopback network interface (ie. in case, eth0)
   • query ip address of interface (in case, 192.168.20.20 or fe80:0:0:0:21c:c0ff:fef2:ba89%2)
   • resolve ip address. can see hosts file, 192.168.20.20 correctly resolves maxim-desktop, there no hostname corresponding ipv6 address.

2. ipv6 addresses beginning fe80 (or, precise, addresses in fe80::/10 network) link-local addresses, , %2 denotes network interface system should use.