Internet Addresses - Java Network Programming - page 103

The isLoopbackAddress() method returns true if the address is the loopback address,
false otherwise. The loopback address connects to the same computer directly in the IP
layer without using any physical hardware. Thus, connecting to the loopback address
enables tests to bypass potentially buggy or nonexistent Ethernet, PPP, and other drivers,
helping to isolate problems. Connecting to the loopback address is not the same as
connecting to the system's normal IP address from the same system. In IPv4, this address
is 127.0.0.1. In IPv6, this address is 0:0:0:0:0:0:0:1 (a.k.a. ::1).
The isLinkLocalAddress() method returns true if the address is an IPv6 link-local
address, false otherwise. This is an address used to help IPv6 networks self-configure,
much like DHCP on IPv4 networks but without necessarily using a server. Routers do
not forward packets addressed to a link-local address beyond the local subnet. All link-
local addresses begin with the eight bytes FE80:0000:0000:0000. The next eight bytes
are filled with a local address, often copied from the Ethernet MAC address assigned
by the Ethernet card manufacturer.
The isSiteLocalAddress() method returns true if the address is an IPv6 site-local
address, false otherwise. Site-local addresses are similar to link-local addresses except
that they may be forwarded by routers within a site or campus but should not be for‐
warded beyond that site. Site-local addresses begin with the eight bytes
FEC0:0000:0000:0000. The next eight bytes are filled with a local address, often copied
from the Ethernet MAC address assigned by the Ethernet card manufacturer.
The isMulticastAddress() method returns true if the address is a multicast address,
false otherwise. Multicasting broadcasts content to all subscribed computers rather than
to one particular computer. In IPv4, multicast addresses all fall in the range 224.0.0.0
to 239.255.255.255. In IPv6, they all begin with byte FF. Multicasting will be discussed
in Chapter 13 .
The isMCGlobal() method returns true if the address is a global multicast address, false
otherwise. A global multicast address may have subscribers around the world. All mul‐
ticast addresses begin with FF. In IPv6, global multicast addresses begin with FF0E or
FF1E depending on whether the multicast address is a well known permanently assigned
address or a transient address. In IPv4, all multicast addresses have global scope, at least
as far as this method is concerned. As you'll see in Chapter 13 , IPv4 uses time-to-live
(TTL) values to control scope rather than addressing.
The isMCOrgLocal() method returns true if the address is an organization-wide mul‐
ticast address, false otherwise. An organization-wide multicast address may have sub‐
scribers within all the sites of a company or organization, but not outside that organi‐
zation. Organization multicast addresses begin with FF08 or FF18, depending on
whether the multicast address is a well known permanently assigned address or a tran‐
sient address.