CompTIA Network+ Preparation · lesson 8 of 30 · 25 min
IPv6 Fundamentals
IPv6 uses 128-bit addresses written as eight groups of four hexadecimal digits separated by colons: 2001:0db8:85a3:0000:0000:8a2e:0370:7334.
Abbreviation rules: 1. Leading zeros in each group can be omitted: 0db8 → db8. 2. One consecutive sequence of all-zero groups can be replaced with :: (double colon). Example: 2001:db8::1 = 2001:0db8:0000:0000:0000:0000:0000:0001. The :: can only appear once.
IPv6 address space: 2^128 = 340 undecillion addresses. Enough for every atom on Earth to have multiple addresses.
No broadcast in IPv6 — IPv6 uses multicast instead of broadcast. All-nodes multicast: ff02::1. All-routers multicast: ff02::2.
No ARP in IPv6 — replaced by NDP (Neighbor Discovery Protocol) using ICMPv6 messages.
IPv6 Address Types
Global Unicast (GUA) — publicly routable IPv6 addresses. Start with 2000::/3 (currently 2001::/16 range in use). Equivalent to public IPv4 addresses.
Link-Local — fe80::/10. Automatically configured on every IPv6 interface. Only valid on the local link — not routed. Used for NDP and router discovery. Always present even without global address.
Unique Local (ULA) — fc00::/7 (fd00::/8 in practice). Private IPv6 addresses — not routed on the internet. Equivalent to RFC 1918 private IPv4.
Loopback — ::1/128. Equivalent to 127.0.0.1 in IPv4.
Multicast — ff00::/8. Replaces IPv4 broadcast. Solicited-node multicast: ff02::1:ffxx:xxxx (used by NDP for address resolution).
IPv6 Autoconfiguration
SLAAC (Stateless Address Autoconfiguration) — devices configure their own IPv6 address without a DHCP server. Process: 1. Device generates a link-local address. 2. Sends Router Solicitation (RS) to ff02::2. 3. Router replies with Router Advertisement (RA) containing the network prefix. 4. Device combines prefix + interface ID (from MAC via EUI-64) to form its global address.
EUI-64 — method to derive a 64-bit interface ID from a 48-bit MAC address. Insert fffe in the middle and flip the 7th bit. Example: MAC 00:1A:2B:3C:4D:5E → EUI-64: 021A:2Bff:fe3C:4D5E.
DHCPv6 — stateful (assigns full address like DHCPv4) or stateless (provides DNS/options only, SLAAC handles address). Uses UDP ports 546 (client) and 547 (server).
NDP (Neighbor Discovery Protocol) — ICMPv6-based. Replaces ARP. Key messages: Router Solicitation (RS), Router Advertisement (RA), Neighbor Solicitation (NS), Neighbor Advertisement (NA).
Exam Tip
IPv6 has no broadcast — uses multicast. Link-local (fe80::/10) is always auto-configured. SLAAC uses RA from routers + EUI-64 for the interface ID. DHCPv6 uses ports 546/547.
Key Terms
Key Terms
Knowledge Check — 10 Questions
Network+ — IPv6 Addressing
IPv6 addresses are how many bits long?
- 32
- 64
- 128
- 256
Answer: 128
IPv6 = 128 bits, written as 8 groups of 4 hex digits. IPv4 = 32 bits. The larger space solves IPv4 exhaustion.
Which IPv6 address type is automatically configured on every interface?
- Global Unicast
- Unique Local
- Link-Local (fe80::/10)
- Multicast
Answer: Link-Local (fe80::/10)
Link-local addresses (fe80::/10) are auto-configured on every IPv6-enabled interface — always present, used for NDP and local communication.
IPv6 replaces broadcast with:
- Anycast
- Unicast
- Multicast
- Broadcast still exists in IPv6
- Answer: Multicast
IPv6 has no broadcast. Multicast groups replace broadcast — all-nodes (ff02::1), all-routers (ff02::2), solicited-node multicast. SLAAC allows devices to configure IPv6 addresses without:
- A router
- A DHCP server
- An interface
- A MAC address
- Answer: A DHCP server
SLAAC = Stateless Address Autoconfiguration. Devices use Router Advertisements and EUI-64 to self-configure — no DHCP server needed. The IPv6 loopback address is:
- ::0
- ::1
- fe80::1
- ff02::1
- Answer: ::1
::1 is the IPv6 loopback (equivalent to 127.0.0.1). The full form is 0000:0000:0000:0000:0000:0000:0000:0001. Unique Local (fc00::/7) IPv6 addresses are equivalent to:
- Public IPv4
- RFC 1918 private IPv4
- APIPA
- Loopback
- Answer: RFC 1918 private IPv4
Unique Local addresses (fd00::/8 in practice) are private IPv6 — not routed on the internet, equivalent to 10.x, 172.16.x, 192.168.x.
NDP (Neighbor Discovery Protocol) replaces which IPv4 protocol?
- DHCP
- DNS
- ARP
- ICMP
Answer: ARP
NDP uses ICMPv6 to perform address resolution (replacing ARP), router discovery, and prefix advertisement.
DHCPv6 uses which ports?
- 67/68
- 546/547
- 53/54
- 443/444
Answer: 546/547
DHCPv6: client port 546, server port 547. Compare to DHCPv4: client 68, server 67.
The double colon (::) in an IPv6 address represents:
- A separator between network and host
- One consecutive sequence of all-zero groups
- The end of the address
- A private address indicator
- Answer: One consecutive sequence of all-zero groups
:: replaces one or more consecutive groups of all zeros. It can only appear once in an address to avoid ambiguity.
EUI-64 derives a 64-bit interface ID from a 48-bit _____ address.
Answer: MAC
EUI-64 takes the 48-bit MAC address, inserts fffe in the middle, and flips the 7th bit to create the 64-bit interface ID used in SLAAC.
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