
82 Part One • Theory
inasmuch as these tunnels treat the global IPv4 Internet as a broadcast
medium. Any significant deployment is likely to affect performance
on the IPv4 Internet.
In addition to tunnels, IPv6/IPv4 interoperability requires the use of nodes
that can handle both protocols at the same time, as discussed next.
5.3 IPv4/IPv6 Dual-Stack
The tenacity of legacy systems, as demonstrated by the years of prepara-
tion required to allay Year 2000 fears, should be underestimated at our
peril. IPv4 will be with us for a long time, even as some or all of the rest
of the networked world upgrades to IPv6. During that time, the upgraded
systems will