CCNA Foundations: IPv6 Addressing — Put a /64 on the Wire

Archive lab

Bring IPv6 up alongside the already-working IPv4 baseline. You will enable IPv6 unicast routing on both routers, put a unique 2001:db8::/64 on each site LAN, put a /127 on the router-to-router transit, and address the dual-homed workstation on both of the LANs it is plugged into plus its IPv6 default route. Verify that IPv6 reaches both on-link gateways and, through the default route, the near router's transit address — while the far router's transit address stays unreachable over IPv6 and reachable over IPv4, because no IPv6 routing between the sites exists yet.

Learning objectives

• Enable IPv6 unicast routing on Cisco IOS routers
• Assign a unique /64 to each LAN interface and a /127 to the point-to-point transit
• Statically address a dual-homed dual-stack host on both of its LANs and give it an IPv6 default route
• Verify IPv6 interface state, neighbor discovery and reachability, and explain which pings connected routes alone can and cannot carry, while IPv4 keeps working

Troubleshooting focus

• If IPv6 pings fail, first confirm ipv6 unicast-routing is present on BOTH routers; without it a router holds IPv6 addresses but forwards nothing between its interfaces.
• Each segment must use its own /64: 2001:db8:10:10::/64 at Site A and 2001:db8:20:20::/64 at Site B. Reusing one prefix on both segments breaks on-link determination for every host.
• The /127 belongs only on the router-to-router transit, and both ends must agree. A mask typo there leaves the two routers in different prefixes and the transit never appears as connected on both sides.
• CLIENT-A10 is dual-homed: eth0 must carry the Site A prefix and eth1 the Site B prefix. The wrong site's address on a NIC strands that interface even though the cable is fine.
• If the host reaches both gateways but not 2001:db8:12:1::1, it has addresses and no IPv6 default route. If it reaches 2001:db8:12:1::1 but not 2001:db8:12:1::2, that is the correct result today — RTR-B-EDGE has no route back to Site A's /64.
• Use show ipv6 neighbors on a router to confirm ND resolved the host; a missing or INCMP entry points at an access-VLAN mismatch on the switch or a NIC addressed out of the wrong /64.