Read the address
An IPv6 address contains eight 16-bit groups written in hexadecimal. Leading zeros in a group may be omitted. One run of zero groups can be compressed with a double colon.
- 2001:db8:10::25 is a documentation address, safe for examples.
- A /64 prefix leaves 64 bits for the interface identifier.
- ::1 is loopback; :: is the unspecified address.
- fe80::/10 is link-local; an interface scope may be needed when using it.
Addressing is more than DHCP
Router advertisements announce on-link prefixes and default routers. SLAAC can configure addresses without a DHCPv6 address lease. DHCPv6 can provide addresses or other settings, depending on the network.
- A host can have several IPv6 addresses at once.
- Neighbour discovery uses ICMPv6; blanket blocking can break basic connectivity.
- IPv6 has multicast but no broadcast.
- A /127 can be used on point-to-point router links.
Roll out dual stack deliberately
Dual stack runs IPv4 and IPv6 together. Test both paths; success over one family can hide a fault in the other.
- Publish AAAA records only when the service is reachable over IPv6.
- Apply equivalent firewall policy to both address families.
- Verify DNS, routes, path MTU and monitoring for each family.
- NAT is not a security boundary. Use explicit stateful ingress rules.