📘 03-03: IPv6 Addressing¶
💡 Why IPv6?¶
IPv4's 32-bit space (~4.3 billion addresses) is exhausted. IPv6 uses 128 bits, providing a virtually unlimited address space.
📌 Format¶
Eight groups (hextets) of four hex digits, separated by colons:
🔹 Compression rules¶
- Drop leading zeros in each hextet:
0db8→db8,0000→0. - Replace one run of consecutive all-zero hextets with
::(only once).
📌 Address Types¶
| Prefix | Type | Notes |
|---|---|---|
2000::/3 |
Global unicast | Internet-routable |
fe80::/10 |
Link-local | Valid only on the local link |
::1/128 |
Loopback | Equivalent to 127.0.0.1 |
ff00::/8 |
Multicast | No broadcast in IPv6 |
fc00::/7 |
Unique local | Private-like (ULA) |
📌 Interface ID & Autoconfiguration¶
- A LAN subnet is almost always /64: first 64 bits = network prefix, last 64 = interface ID.
- EUI-64 derives the interface ID from the 48-bit MAC (insert
FFFE, flip U/L bit). - SLAAC lets a host build its own address from the Router Advertisement prefix + interface ID — no DHCP needed.
- NDP (ICMPv6) replaces ARP for neighbor/router discovery.
Tip
Key idea — IPv6 = 128 bits, eight hextets, compressed with :: (once) and dropped leading zeros. LANs use /64; hosts can self-configure via SLAAC/EUI-64.
See also: IPv4 Addressing, Subnets in IPv6
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