Inet4Address

port of java.net.Inet4Address

This class represents an Internet Protocol version 4 (IPv4) address. Defined by RFC 790: Assigned Numbers, RFC 1918: Address Allocation for Private Internets, and RFC 2365: Administratively Scoped IP Multicast

Textual representation of IPv4 addresses

Textual representation of IPv4 address used as input to methods takes one of the following forms:

• {@code d.d.d.d}
• {@code d.d.d}
• {@code d.d}
• {@code d}

When four parts are specified, each is interpreted as a byte of data and assigned, from left to right, to the four bytes of an IPv4 address.

When a three part address is specified, the last part is interpreted as a 16-bit quantity and placed in the right most two bytes of the network address. This makes the three part address format convenient for specifying Class B network addresses as 128.net.host.

When a two part address is supplied, the last part is interpreted as a 24-bit quantity and placed in the right most three bytes of the network address. This makes the two part address format convenient for specifying Class A network addresses as net.host.

When only one part is given, the value is stored directly in the network address without any byte rearrangement.

For example, the following (decimal) forms are supported by the methods {@link Inet4Address#ofLiteral(String)} and {@link InetAddress#getByName(String)} which are capable of parsing textual representations of IPv4 addresses: {@snippet : // Dotted-decimal 'd.d.d.d' form with four part address literal InetAddress.getByName("007.008.009.010"); // ==> /7.8.9.10 InetAddress.getByName("127.0.1.1"); // ==> /127.0.1.1

// Dotted-decimal 'd.d.d' form with three part address literal, // the last part is placed in the right most two bytes // of the constructed address InetAddress.getByName("127.0.257"); // ==> /127.0.1.1

// Dotted-decimal 'd.d' form with two part address literal, // the last part is placed in the right most three bytes // of the constructed address Inet4Address.ofLiteral("127.257"); // ==> /127.0.1.1

// 'd' form with one decimal value that is stored directly in // the constructed address bytes without any rearrangement Inet4Address.ofLiteral("02130706689"); // ==> /127.0.1.1 }

The above forms adhere to "strict" decimal-only syntax. Additionally, the {@link Inet4Address#ofPosixLiteral(String)} method implements a POSIX {@code inet_addr} compatible "loose" parsing algorithm, allowing octal and hexadecimal address segments. Please refer to RFC 6943: Issues in Identifier Comparison for Security Purposes. Aside from {@code Inet4Address.ofPosixLiteral(String)}, all methods only support strict decimal parsing.

For methods that return a textual representation as output value, the first form, i.e. a dotted-quad string in strict decimal notation, is used.

The Scope of a Multicast Address

Historically the IPv4 TTL field in the IP header has doubled as a multicast scope field: a TTL of 0 means node-local, 1 means link-local, up through 32 means site-local, up through 64 means region-local, up through 128 means continent-local, and up through 255 are global. However, the administrative scoping is preferred. Please refer to RFC 2365: Administratively Scoped IP Multicast