IPv6 Addressing
IPv6 questions are usually recognition rather than calculation: which type of address is this, and what is the shortened form. Both tables below answer that directly.
IPv6 Addressing · firsttry.app/cheatsheets/ipv6-basics · original reference written from published exam objectives. Not affiliated with any certification body.
Address types
| Type | Prefix | Scope and use |
|---|---|---|
| Global unicast | 2000::/3 | Routable on the internet |
| Unique local | FC00::/7, in practice FD00::/8 | Private, not routed on the internet |
| Link-local | FE80::/10 | One link only. Every interface has one |
| Multicast | FF00::/8 | One to many |
| All nodes multicast | FF02::1 | Every node on the link |
| All routers multicast | FF02::2 | Every router on the link |
| Solicited-node multicast | FF02::1:FF00:0/104 | Used by neighbour discovery |
| Loopback | ::1 | The host itself |
| Unspecified | :: | No address yet, used during configuration |
Shortening rules
| Rule | Full | Short |
|---|---|---|
| Drop leading zeros in a group | 2001:0db8:0000:0042 | 2001:db8:0:42 |
| Replace one run of zero groups with :: | 2001:db8:0:0:0:0:0:1 | 2001:db8::1 |
| Only one :: per address | 2001:0:0:1:0:0:0:1 | 2001:0:0:1::1 |
| Loopback | 0000:0000:0000:0000:0000:0000:0000:0001 | ::1 |
| All zeros | 0000:0000:0000:0000:0000:0000:0000:0000 | :: |
Structure and configuration
| Term | Detail |
|---|---|
| Address length | 128 bits, written as eight groups of four hex digits |
| Typical subnet | /64. The last 64 bits are the interface identifier |
| Typical site allocation | /48, giving 65,536 /64 subnets |
| SLAAC | The host builds its own address from a router advertisement |
| EUI-64 | Interface ID derived from the MAC, with FFFE inserted |
| DHCPv6 | Stateful assignment, used where SLAAC is not enough |
| Neighbour discovery | Replaces ARP. Uses ICMPv6 |
| No broadcast | IPv6 has none. Multicast does the job |
Transition mechanisms
| Method | How it works |
|---|---|
| Dual stack | Run IPv4 and IPv6 together. The preferred approach |
| 6to4 / Teredo | Tunnel IPv6 inside IPv4 |
| GRE tunnel | Generic tunnel carrying IPv6 across an IPv4 network |
| NAT64 / DNS64 | Translate between IPv6-only clients and IPv4 servers |
Exams covered
Try it here
Three verified practice questions on this material. Answer one, and see the official page behind the answer.
6-5Automation and Programmability
Device configuration is exchanged over NETCONF. How is the configuration data encoded?
3-2Network Operations
A switch sends unsolicited alerts to the manager when a link drops. Which UDP port receives those?
Architecture
From how many of the four character classes must an access point global password draw?
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