Explain IPv6 protocol architecture and differences from IPv4
Master hexadecimal notation, compression rules, and address types
Analyze fixed header structure and extension headers
Evaluate dual-stack, tunneling, and translation mechanisms
IPv4 provides only 4.3 billion addresses (2³²). With mobile devices, IoT, and cloud computing, addresses depleted by 2011.
IPv6 offers 340 undecillion addresses (2¹²⁸) = 340,282,366,920,938,463,463,374,607,431,768,211,456
Fixed 40-byte header (vs variable IPv4), no checksum recalculation at every hop, native IPsec support, and improved multicast.
Analogy: If IPv4 addresses were grains of sand, they would fill a dump truck. IPv6 addresses would fill the entire Earth 10⁹ times over.
Note: Can only be used once per address to avoid ambiguity
One-to-one communication. Identifies a single interface.
2000::/3 (2000-3FFF)
Routable addresses, equivalent to IPv4 public addresses
FE80::/10
Auto-configured, non-routable, used for neighbor discovery
FC00::/7
Private addressing, similar to IPv4 RFC 1918
::1
One-to-many communication. Replaces IPv4 broadcast.
FF00::/8
FF02::1 (All nodes)
FF02::2 (All routers)
FF02::1:FFxx:xxxx
Used for Neighbor Discovery Protocol (NDP)
One-to-nearest communication. Identifies multiple interfaces.
• Same address on multiple nodes
• Delivered to "nearest" (lowest metric)
• Used for load balancing and redundancy
DNS root servers, CDN nodes, anycast DNS resolvers
Indistinguishable from unicast syntactically. Configured by assigning same address to multiple interfaces.
IPv6 typically uses a 64-bit interface identifier derived from the 48-bit MAC address using the Extended Unique Identifier (EUI-64) format, modified for IPv6.
Split the 48-bit MAC address in half
Insert FFFE (16 bits) in the middle
Invert the 7th bit (Universal/Local bit)
| Feature | IPv4 | IPv6 |
|---|---|---|
| Header Size | 20-60 bytes (variable) | 40 bytes (fixed) |
| Checksum | Header checksum (recalculated at each hop) | None (handled by upper layers) |
| Fragmentation | Routers and hosts can fragment | Only source host fragments (Path MTU Discovery) |
| Options | In header (variable, rarely used) | Extension headers (chained) |
| Address Resolution | ARP (Broadcast) | NDP (Neighbor Discovery Protocol) - Multicast |
| Configuration | Manual or DHCP | Auto-configuration (SLAAC) or DHCPv6 |
NDP (RFC 4861) replaces IPv4 ARP, ICMP Router Discovery, and ICMP Redirect. Uses ICMPv6 messages and solicited-node multicast for efficiency.
Hosts send to FF02::2 to discover routers on the link
Rulers announce presence, prefixes, MTU, hop limit. Used for SLAAC.
Resolve IPv6 to MAC (replaces ARP request). Sent to solicited-node multicast.
Response to NS with MAC address. Also sent when MAC changes.
Host generates EUI-64 from MAC and prepends FE80::/10
Sends NS to own solicited-node multicast address to ensure uniqueness
Send RS to FF02::2, receive RA with network prefix (e.g., 2001:DB8::/64)
Combine prefix + EUI-64
Run IPv4 and IPv6 simultaneously on same infrastructure. Hosts and routers process both protocols.
Encapsulate IPv6 packets in IPv4 headers to traverse IPv4-only networks (6in4, 6to4, Teredo).
Translate between IPv4 and IPv6 at protocol boundary. Allows IPv6-only clients to reach IPv4 servers.
Format: xx:xx:xx:xx:xx:xx or xx-xx-xx-xx-xx-xx