NLnet Labs Cisco Systems Cisco Systems During the transition from IPv4 to IPv6 both protocols will be used simultaneously. Most nodes will support both protocols and will be able to communicate via both IPv4 and IPv6 transport. Problems arise when a node only supports IPv4 and it wants to communicate with a node that only supports IPv6. Translation between the two IP protocols might be needed in some cases. This memo discusses the problems involved in translation between IPv4 and IPv6.