What does InetAddress.isSiteLocalAddress() actually mean?

Question

Here is some code to determine the local host name that is supposed to work on a multi-homed box:

 /**
 * Work out the first local host name by iterating the network interfaces
 * 
 * @return
 * @throws SocketException
 */
private String findFirstLocalHostName() throws SocketException {

    Enumeration<NetworkInterface> ifaces = NetworkInterface.getNetworkInterfaces();
    while (ifaces.hasMoreElements()) {
        NetworkInterface iface = ifaces.nextElement();
        Enumeration<InetAddress> addresses = iface.getInetAddresses();
        while (addresses.hasMoreElements()) {
            InetAddress add = addresses.nextElement();
            if (!add.isLoopbackAddress() && add.isSiteLocalAddress()) {
                return add.getHostName();
            }
        }
    }
    throw new RuntimeException("Failed to determine local hostname");
}

Does the call to isSiteLocalAddress introduce a bug? I can't find any useful information about this method, but I have a feeling that it relates to IP v 6 only and is deprecated.

For clarity, I didn't mean that the method was deprecated... just the notion of "site local" address in IPv6 as per http://www.ietf.org/rfc/rfc3879.txt — TiGz, Apr 11 '11 at 10:23

Joachim Sauer · Accepted Answer · 2022-07-10T11:40:49.333

28

The method is definitely not deprecated and it's definitely not just used in IPv6.

In IPv4 there are 3 network address ranges that are defined for site-local addresses: 10/8, 172.16/12 and 192.168/16.

Reading Inet4Address.isSiteLocalAddress() shows that addresses from exactly those 3 networks will return true on those methods.

IPv6 has a similar concept, here these addresses are called unique local addresses.

Effectively this tells you if the address you have is definitely not a public one (note that even if this method returns false, the address might still not be public).

edited Jul 10 '22 at 11:40

answered Apr 11 '11 at 09:38

Joachim Sauer

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see [here](http://books.google.co.in/books?id=NyxObrhTv5oC&lpg=PT187&dq=InetAddress.isSiteLocalAddress()&pg=PT186#v=onepage&q&f=false). it returns true if the address is an IPv6 site-local address. – Prince John Wesley Apr 11 '11 at 09:43
@John: yes, I know that there is a similar meaning in IPv6 as well, but I don't know the specifics of it. But since the question implied that it's IPv6-only, I wanted to clarify that aspect. (By the way, I can't read the page you linked to). – Joachim Sauer Apr 11 '11 at 09:46

score 1 · Answer 2 · answered Apr 11 '11 at 09:39

Looking at the implementation...

For an Inet4Address, it checks to see if it's one of the RFC1918 "unrouteable" addresses: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16.

For an Inet6Address, it checks the first two octets to see if it's a real "site local" address.

score 0 · Answer 3 · answered Jun 24 '15 at 20:32

I just came across what I believe is a similar problem: trying to determine what IPv6 I should use for LAN comuncation:

IMHO, Inet6Address.isSiteLocalAddress() is useless. Given that the 0xFEC0 prefix has been depricated by RFC 3879 as @tigz mentioned. I have yet to see any device (android, win, osx) actually have a 0xFEC0 (with limited testing)

//from java.net.Inet6Address (1.8.0_45) boolean isSiteLocalAddress() { return ((ipaddress[0] & 0xff) == 0xfe && (ipaddress[1] & 0xc0) == 0xc0); }
0xFE80 address although not supposed be used for traffic (from my understanding and reading (www.cisco.com)) did work for LAN communication with my single router (ping6, curl, http).
My Global Unicast (which is just another name for public IP) 2601::/20 from Comcast worked for my LAN communication. So I would say that this is the correct address to use.

Prefix table: www.iana.org

score 0 · Answer 4 · answered Apr 15 '11 at 16:13

0

'Site local' is a deprecated name for private IP space. (Some nuances, but basically right.) See RFC 1918.

answered Apr 15 '11 at 16:13

jmac

1

score -1 · Answer 5 · edited Apr 11 '11 at 09:49

-1

As far as I know the isSiteLocalAddress method is not deprecated.

isSiteLocalAddress - Explanation

indicating if the InetAddress is a site local address; or false if address is not a site local unicast address.

The InetAddress even have two direct subclasses;

Inet4Address and Inet6Address

The best bet is to read the JavaDocs.

Which version of the JDK are you using?

edited Apr 11 '11 at 09:49

Joachim Sauer

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answered Apr 11 '11 at 09:40

Koekiebox

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What does InetAddress.isSiteLocalAddress() actually mean?

5 Answers5