Strange symbols in IPv6 address in Java

Question

When I call method NetworkInterface.getInetAddresses(), i get the following string:

"fe80:0:0:0:f06c:31b8:cd17:5a44%5"

I wonder what %5 means here? Is it possible to het IPv6 address without this %5?

See also http://stackoverflow.com/questions/5746082/ipv6-link-local-address-format — mpontillo, Jan 29 '13 at 15:51

score 6 · Accepted Answer · edited Jan 28 '13 at 19:57

It's explained here:

Inet6Adress - Format

The general format for specifying the scope_id is the following:
*IPv6-address%scope_id*
The IPv6-address is a literal IPv6 address as described above. The scope_id refers to an interface on the local system, and it can be specified in two ways.

As a numeric identifier. This must be a positive integer that identifies the particular interface and scope as understood by the system. Usually, the numeric values can be determined through administration tools on the system. Each interface may have multiple values, one for each scope. If the scope is unspecified, then the default value used is zero.

As a string. This must be the exact string that is returned by NetworkInterface.getName() for the particular interface in question. When an Inet6Address is created in this way, the numeric scope-id is determined at the time the object is created by querying the relevant NetworkInterface.

Note also, that the numeric scope_id can be retrieved from Inet6Address instances returned from the NetworkInterface class. This can be used to find out the current scope ids configured on the system.

score 2 · Answer 2 · answered Jan 28 '13 at 19:50

2

The 5 is the zone index. The % is used to separate it.

A Windows machine would have one such as %1.

A Unix machine would have one such as %eth0. Using the interface name as the zone index.

answered Jan 28 '13 at 19:50

3

Can you link to the documentation please? – John Dvorak Jan 28 '13 at 19:51
Is this index important or I can trim it? – Anthony Jan 28 '13 at 19:53
I'm afraid the zone index is actually an IPv4 thing (it's called differently in IPv6 – John Dvorak Jan 28 '13 at 19:54

score 0 · Answer 3 · answered Dec 18 '17 at 02:11

The % sign denotes the Ipv6 zone or scope id.

The open-source IPAddress Java library will validate all standard representations of IPv6. You can extract the zone as shown. Disclaimer: I am the project manager of that library.

Code example:

        try {
            IPAddressString str = new IPAddressString("fe80:0:0:0:f06c:31b8:cd17:5a44%5");
            IPAddress addr = str.toAddress();
            if(addr.isIPv6() || addr.isIPv6Convertible()) {
                IPv6Address ipv6Addr = addr.toIPv6();
                String zone = ipv6Addr.getZone();
                IPv6Address noZoneAddr = new IPv6Address(ipv6Addr.getSection());
                System.out.println("zone is " + zone + " for address " + noZoneAddr);
            }
            //use address
        } catch(AddressStringException e) {
            //e.getMessage has validation error
        }

Output:

        zone is 5 for address fe80:0:0:0:f06c:31b8:cd17:5a44

Strange symbols in IPv6 address in Java

3 Answers3