Understand prefixes and local next hops.
A larger address space
IPv6 uses 128-bit addresses written in hexadecimal groups. Leading zeros in a group can be omitted. One consecutive run of zero groups can be compressed with ::. For example, 2001:db8:10::1 is an address in the documentation range used in these lessons.
Global unicast addresses are used for global routing. Unique local addresses come from fc00::/7, with locally assigned addresses commonly beginning fd. Link-local addresses use fe80::/10 and stay on the local link. Multicast reaches a group; anycast uses an address assigned to multiple interfaces with routing choosing a reachable instance. IPv6 has no broadcast address.
IPv6 Neighbor Discovery operation
IPv6 Neighbor Discovery uses ICMPv6 messages instead of IPv4 ARP. Router advertisements tell hosts about routers and prefixes. SLAAC lets a host form an address using advertised information; DHCPv6 can supply addresses or other settings, depending on the design. The default router is learned through router advertisements, not a DHCPv6 default-gateway option.
Ordinary SLAAC LANs use /64 prefixes. Interface identifiers may use stable or privacy methods; do not assume every device derives an identifier from its MAC. Modified EUI-64 inserts fffe into a 48-bit MAC and flips the universal/local bit. It is one method, not a requirement for all IPv6 addresses.
Verification commands
Use these viewing commands to inspect the idea in this lesson. Start in the environment shown above each example.
show ipv6 interface brief
show ipv6 neighborsCommand reference · enter in the stated environment; output varies by device.
Practical exercise
Expand 2001:db8:10::25 into eight groups. Explain whether an fe80:: address should be forwarded across routers.
Show the answer and explanation
Expanded: 2001:0db8:0010:0000:0000:0000:0000:0025. Link-local addresses are scoped to a link and are not forwarded between links.
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