This document discusses the transition from IPv4 to IPv6. It begins by providing background on IPv4 and addressing its limitations, such as address depletion. IPv6 was created to replace IPv4 and solve these issues by providing vastly more IP addresses. However, a long transition is expected as networks gradually migrate to IPv6. Technologies like NAT-PT allow IPv6-only and IPv4-only networks to communicate during the transition period. The document then covers IP addressing schemes, comparing IPv4 and IPv6, and routing concepts relevant to the migration.