IPv6 uses 128-bit addresses, written as eight groups of four hexadecimal digits separated by colons. It answers the exhaustion of IPv4 addresses with a practically unlimited address space.

Writing rules

• You drop the leading zeros of each group.
• You replace one run of all-zero groups with ::, only once.
• The /64 prefix is the standard subnet size.
• Useful types: link-local (fe80::/10) and global unicast (2000::/3).

R1> enable
R1# configure terminal
R1(config)# ipv6 unicast-routing
R1(config)# interface gigabitEthernet 0/0
R1(config-if)# ipv6 address 2001:db8:acad:1::1/64
R1(config-if)# no shutdown
R1(config-if)# end
R1# show ipv6 interface brief

The ipv6 unicast-routing command turns on IPv6 routing on the router. To create IPv6 subnets you vary the subnet field (the 16 bits before the interface ID of a /64), for example acad:1, acad:2, acad:3. Each /64 stays enormous, so you never trim the host portion.

Key point: IPv6 = 128 bits, /64 subnets, :: only once; remember to enable ipv6 unicast-routing. See Lab 13 – Configuring IPv6 addressing.