Dual stack is how IPv6 actually arrives: one interface carrying IPv4 and IPv6 at the same time, both live, neither aware of the other. That last part is what costs people hours. The two protocols share a cable and a configuration mode and nothing else — separate addressing, separate routing tables, separate access lists, separate neighbour resolution. A device can be perfectly reachable over IPv4 while its IPv6 side is unaddressed, unrouted or entirely unfiltered, and every IPv4 test you run will still pass.
These labs make you configure and verify both halves rather than let one stand in for the other. You'll put IPv4 and IPv6 on the same interfaces, size the prefixes the links need, add IPv6 static routes and a default route out, relay DHCPv6 to a server on another subnet, run OSPFv3 in parallel with an existing OSPFv2 baseline, and finish with a dual-stacked site filtered by an IPv6 ACL. Verification is deliberately doubled — show ip route beside show ipv6 route, show ip interface brief beside show ipv6 interface brief — because a healthy v4 column says nothing about the v6 one. Grading checks each protocol on its own, so a lab where only IPv4 works does not pass.
