Dual Stack

• Keep v4, add v6 support to OS

• • Multiprotocol stacks are very common (IPX, Appletalk)
  • New OS release ships with v6, no extra cost
  • • Windows XP
    • Linux 2.x

• Apps or libraries choose version of IP to use

• • Initiators use v6 if DNS response is AAAA or A6 record
  • Responders use same version an initiating packet

• Allows coexistence and gradual, application by application, upgrade to v6