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IPv6 Overview and Addressing

Jun 12, 2025

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Overview

This lecture wraps up IPv6 topics for the CCNA by covering address representation, the IPv6 header, Neighbor Discovery Protocol (NDP), SLAAC, and IPv6 static routing concepts.

IPv6 Address Representation Rules

  • RFC 5952 standardizes IPv6 address text representation.
  • Leading zeros in each quartet must be removed.
  • Use double colon (::) to shorten the longest string of all-0 quartets, preferring the leftmost if tied.
  • Hexadecimal a-f must be written in lowercase.

IPv6 Header Overview

  • IPv6 header has a fixed size of 40 bytes (simpler than IPv4).
  • Key fields: Version (4 bits, always 6), Traffic Class (QoS, 8 bits), Flow Label (20 bits), Payload Length (16 bits), Next Header (8 bits), Hop Limit (8 bits, decremented per router), Source/Destination Address (128 bits each).

Neighbor Discovery Protocol (NDP)

  • NDP replaces ARP in IPv6, using ICMPv6 messages.
  • Uses solicited-node multicast addresses (ff02::1:ff + last 6 hex digits of target unicast address).
  • Key ICMPv6 types: 133 (Router Solicitation), 134 (Router Advertisement), 135 (Neighbor Solicitation/NS), 136 (Neighbor Advertisement/NA).
  • NS is multicast (efficient) vs. ARP which is broadcast.
  • IPv6 neighbor table replaces ARP table; "show ipv6 neighbor" displays it.

SLAAC and Duplicate Address Detection (DAD)

  • SLAAC (Stateless Address Auto-configuration) allows devices to auto-configure IPv6 addresses using RS/RA messages.
  • DAD ensures no duplicate IPv6 addresses exist by sending NS to its own solicited-node multicast address and awaiting an NA response.

IPv6 Static Routing Concepts

  • IPv6 routing is similar to IPv4 but configured separately; enable with "ipv6 unicast-routing".
  • Three types of static routes:
    • Directly attached (exit interface only; does NOT work on Ethernet for IPv6).
    • Recursive (next-hop address only).
    • Fully specified (both exit interface and next-hop).
  • Common static routes: network (to subnet), host (to single address, /128), default (::/0), floating (higher AD for backup).
  • With link-local as next-hop, must specify the exit interface.

Key Terms & Definitions

  • RFC — Request for Comments; official documentation for protocols.
  • Solicited-node multicast address — ff02::1:ff + last 6 hex of unicast address; used for neighbor discovery.
  • NDP — Neighbor Discovery Protocol; handles address resolution, router discovery, address auto-configuration, and DAD in IPv6.
  • SLAAC — Stateless Address Auto-configuration; auto-address assignment via network prefix from RA.
  • DAD — Duplicate Address Detection; checks for address conflicts.
  • Administrative Distance (AD) — Route preference value for floating static routes.

Action Items / Next Steps

  • Review Anki flashcards with "ipv6" tag for this and previous IPv6 lectures.
  • Complete the upcoming packet tracer lab on IPv6 static routing.
  • Practice commands for configuring and verifying IPv6 static routes on Cisco devices.

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