Internet Protocol version 6 (IPv6) protocol notes¶

1. Advantages of IPv6 Deployment¶

• Vast Address Space: 128-bit addresses (≈3.4×10³⁸ addresses) eliminate scarcity.

• Simplified Header: Streamlined base header improves router processing efficiency.

• Stateless Address Autoconfiguration (SLAAC): Hosts can self-configure addresses without DHCP.

• Built-in Security: IPsec (authentication/encryption) is mandatory, enhancing end-to-end security.

• Improved Multicast & Anycast: Efficient group communication and service delivery.

• No NAT Required: Restores end-to-end connectivity, simplifying applications.

• Better Mobility Support: Mobile IPv6 handles roaming more effectively.

2. Writing IPv6 Addresses (Best Practices)¶

• Compression: Remove leading zeros in each hextet (16-bit block) and replace the longest consecutive sequence of all-zero hextets with :: (once per address).

  • Example: 2001:0db8:0000:130f:0000:0000:08ec:140b → 2001:db8:0:130f::8ec:140b

• Lowercase: Use lowercase letters (e.g., fd00::1, not FD00::1).

• CIDR Notation: Always include prefix length (e.g., 2001:db8::/32).

3. IPv6 Address Types & Scopes¶

4. Calculating IPv6 Subnets¶

• Subnetting borrows bits from the host portion to create subnets.

• Formula: Number of subnets = 2^(new_prefix - current_prefix)

• Example: How many /64 subnets in a /56?
  2^(64-56) = 2^8 = 256 subnets.

• Subnet ranges:

  • Base: 2001:db8:abc::/56

  • Subnet 1: 2001:db8:abc:0::/64

  • Subnet 2: 2001:db8:abc:1::/64

  • …

  • Subnet 256: 2001:db8:abc:ff::/64

5. Key IPv6-Related Protocols¶

• NDP (Neighbor Discovery Protocol): Replaces ARP, manages neighbor reachability.

• SLAAC (Stateless Address Autoconfiguration): Hosts generate addresses using RA messages.

• DHCPv6: Stateful address/config assignment (complements SLAAC).

• ICMPv6: Error reporting and diagnostic functions (e.g., ping6).

• PMTUD (Path MTU Discovery): Determines optimal packet size for a path.

6. Characteristics & Security Concerns¶

• Characteristics:

  • No broadcast (uses multicast).

  • Extension headers for optional features.

  • Simplified fragmentation (handled by source).

• Security Concerns:

  • RA Guard: Needed to block rogue Router Advertisements.

  • DHCPv6 Spoofing: Attackers may impersonate DHCPv6 servers.

  • Extension Header Attacks: Can be used to evade firewalls.

  • Privacy Extensions: Temporary addresses mitigate tracking.

  • Address Scanning Harder: Large address space makes reconnaissance difficult.

7. Creating an IPv6 Addressing Plan¶

1. Get Allocation: Obtain a prefix from ISP/RIR (e.g., /48 for a site).

2. Hierarchical Design:

   • Reserve bits for hierarchy (e.g., region, site, subnet).

   • Example: /48 → /52 per region → /56 per site → /64 per LAN.

3. Subnet Allocation:

   • Assign /64 per VLAN/segment (required for SLAAC).

   • Reserve blocks for future growth (e.g., IoT, guests).

4. Documentation: Record assignments in a subnetting table.

8. IPv6 Transition Mechanisms¶

• Dual Stack: Run IPv4 and IPv6 simultaneously on devices.

• Tunneling: Encapsulate IPv6 in IPv4 (e.g., 6in4, GRE).

• Translation: Convert between v4 and v6 (e.g., NAT64, SIIT).

• Proxying: Use a proxy for protocol translation.

• 464XLAT: Allows IPv4-only apps to work in an IPv6 network (common in mobile networks).

Quick Reference¶

• /48: Typical assignment for a site.

• /56: Typical for residential/large subnet allocation.

• /64: Standard subnet size (one LAN).

• Link-Local: Essential for NDP and SLAAC—always present on interfaces.

Use this cheat sheet for exams, planning, and troubleshooting!