Quiz Entry - updated: 2026.07.14
How do you assign IPv6 subnets to a network topology?
Give each link its own Subnet ID hextet (0001, 0002, ...) under the shared /48 prefix, then configure one /64 per interface — e.g. LAN1 = 2001:db8:acad:1::/64.
IPv6 Subnet Allocation Example:
Given: 2001:db8:acad::/48 global routing prefix Need: 5 subnets (4 LANs + 1 serial link)
Subnet Allocation:
| Segment | Subnet ID | IPv6 Subnet |
|---|---|---|
| LAN 1 (PC1) | 0001 | 2001:db8:acad:1::/64 |
| LAN 2 (PC2) | 0002 | 2001:db8:acad:2::/64 |
| LAN 3 (PC3) | 0003 | 2001:db8:acad:3::/64 |
| LAN 4 (PC4) | 0004 | 2001:db8:acad:4::/64 |
| Serial R1-R2 | 0005 | 2001:db8:acad:5::/64 |
Router Configuration:
R1(config)# interface gigabitethernet 0/0/0
R1(config-if)# ipv6 address 2001:db8:acad:1::1/64
R1(config-if)# no shutdown
R1(config)# interface gigabitethernet 0/0/1
R1(config-if)# ipv6 address 2001:db8:acad:2::1/64
R1(config-if)# no shutdown
R1(config)# interface serial 0/1/0
R1(config-if)# ipv6 address 2001:db8:acad:5::1/64
R1(config-if)# no shutdown
Key insight: With 65,536 available subnets from a /48, address planning is simple!
Go deeper:
How to enable IPv6 on a Cisco router (Study CCNA) — assigning a /64 per interface and verifying with show ipv6 interface.