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05-strategies.md

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Embedding Strategies

When using version 4 and version 6 addresses interchangeably (via the Multi class), version 4 addresses are embedded into version 6 addresses so that both versions are stored as 16-byte binary sequences.

Unfortunately there are several different strategies for embedding a version 4 address into version 6, so this library offers various strategy implementations for the main three:

Strategy Name Implementation Format
6to4-derived Darsyn\IP\Strategy\Derived 2002:XXXX:XXXX:0000:0000:0000:0000:0000
IPv4-compatible Darsyn\IP\Strategy\Compatible 0000:0000:0000:0000:0000:0000:XXXX:XXXX
IPv4-mapped Darsyn\IP\Strategy\Mapped 0000:0000:0000:0000:0000:ffff:XXXX:XXXX

Each embedding strategy implements the Darsyn\IP\Strategy\EmbeddingStrategyInterface which defines methods to:

  • Detect whether a version 4 address is embedded into a version 6 address,
  • Extracting a version 4 address from a version 6 address, and
  • Packing a version 4 address into a version 6 address according to the given strategy.

Specifying a Strategy

This library will automatically use the IPv4-mapped embedding strategy unless otherwise instructed.

An embedding strategy can be specified globally or on a per-instance basis.

<?php
use Darsyn\IP\Strategy;
use Darsyn\IP\Version\Multi as IP;

// Set the IPv4-compatible embedding strategy to be used globally.
IP::setDefaultEmbeddingStrategy(new Strategy\Compatible);

// But for this specific instance use the 6to4-derived embedding strategy.
$ip = IP::factory('127.0.0.1', new Strategy\Derived);