IPv4 Issues and IPv6 Coexistence

IPv4 Issues and the Need for IPv6

• IPv4 runs out of addresses.
• IPv6 is IPv4's successor as it has a larger 128-bit address space.
• IPv6 fixes IPv4's known limitations and offers enhancements.
• IPv6 transition has begun because of internet population growth, limited IPv4 space, NAT issues and IoT.

IPv4 and IPv6 Coexistence

• IPv4 and IPv6 will coexist during the transition period that is expected to last for years.
• The IETF provides protocols/tools for network administrators to migrate networks to IPv6, split into three categories:
  • Dual Stack: Devices run IPv4 and IPv6 protocol stacks simultaneously.
  • Tunneling: Transports an IPv6 packet over an IPv4 network by encapsulating the IPv6 packet inside an IPv4 packet.
  • Translation: NAT64 allows IPv6-enabled devices to communicate with IPv4-enabled devices using translation.

IPv6 Overview

• IPv6 overcomes the limitations of IPv4 limitations with a larger address space.
• IPv6 offers improved packet handling, using simplified headers with fewer fields.
• Private addressing and NAT are no longer needed because of the vast IPv6 addressing space.

Limitations of IPv4

• Address depletion occurred as IPv4 addresses have run out over time.
• End-to-end connectivity issues exist as private addressing and NAT broke direct communications with public addressing.
• Network complexity increased because NAT was intended as a temporary solution.
• Latency and troubleshooting issues are caused by NAT.

IPv6 Packet Header

• IPv6 header is simplified, but the header size is fixed at 40 bytes (or octets).

Key IPv6 Header Fields

• Version: Identifies the IP version (0110 for IPv6).
• Traffic Class: Manages QoS, similar to DiffServ (DS) field.
• Flow Label: Instructs device on handling of identical flow labels in same way, with a 20 bit field.
• Payload Length: Indicates the length of the data portion of the IPv6 packet, using a 16-bit field.
• Next Header: Specifies the next level protocol (ICMP, TCP, UDP, etc.).
• Hop Limit: Replaces the TTL field for Layer 3 hop count.
• Source IPv4 Address: It is a 128 bit source address.
• Destination IPv4 Address: It is a 128 bit destination address.
• Extension Headers: IPv6 packets may contain extension headers that provide optional network layer information, placed between IPv6 header/payload and potentially used for fragmentation, security, and mobility support.
• Routers do not fragment IPv6 packets.

IPv6 Addressing Formats

• IPv6 addresses are 128 bits written in hexadecimal notation.
• IPv6 addresses are case-insensitive.
• Preferred IPv6 format is x:x:x:x:x:x:x:x, where each "x" is four hexadecimal values.
• A hextet refers to a 16-bit segment, or four hexadecimal values, in IPv6.

IPv6 Omission Rules

Rule 1 - Omit Leading Zeros

• Leading zeros can be omitted to reduce IPv6 address notation.
  • 01ab can be represented as 1ab
  • 09f0 can be represented as 9f0
  • 0a00 can be represented as a00
  • 00ab can be represented as ab
• This rule only applies to leading zeros, not trailing zeros, to avoid ambiguity.

Rule 2 - Double Colon

• A double colon (::) replaces a contiguous string of one or more 16-bit hextets consisting of all zeros.
  • 2001:db8:cafe:1:0:0:0:1 (with leading zeros omitted) is 2001:db8:cafe:1::1
• A double colon is only used once in an address to ensure a unique resulting address.

IPv6 Address Types

• Three categories for IPv6 addresses: unicast, multicast, and anycast.
  • Unicast: Uniquely identifies an interface on an IPv6-enabled device.
  • Multicast: Sends a single IPv6 packet to multiple destinations.
  • Anycast: IPv6 unicast address assigned to multiple devices, routing packets to the nearest device with that address.
• IPv6 lacks a broadcast address, but has an IPv6 all-nodes multicast address for similar results.

IPv6 Prefix Length

• Prefix length uses slash notation to indicate the network portion of an IPv6 address.
• IPv6 prefix length ranges from 0 to 128.
• The recommended IPv6 prefix length for LANs and most other networks is /64.
• Use a 64-bit Interface ID, as stateless address autoconfiguration (SLAAC) uses 64 bits for Interface ID and simplifies subnetting.

IPv6 Unicast Addresses

• IPv6 devices commonly have two unicast addresses, unlike IPv4 devices with only one.
• Global Unicast Address (GUA): Similar to a public IPv4 address, globally unique, and internet-routable.
• Link-Local Address (LLA): Required for every IPv6-enabled device, used for communication on the same local link, not routable, and confined to a single link.

Unique Local Address

• Unique local addresses (ULA) in the fc00::/7 to fdff::/7 range are similar to IPv4's RFC 1918 addresses with differences:
  • ULAs are for local addressing within a site or limited sites.
  • ULAs can be used for devices not requiring access to another network.
  • ULAs are not globally routed or translated to a global IPv6 address.
• Using RFC 1918 addresses to secure/hide a network is not the intended use of ULAs.

IPv6 Global Unicast Address

• IPv6 global unicast addresses (GUAs) are globally unique and routable on the IPv6 internet.
  • Currently GUAs with the first three bits of 001 or 2000::/3 are being assigned.
  • GUAs currently begins with a decimal 2 or a 3 which equals 1/8th of the total IPv6 address space.

IPv6 GUA Structure

• Global Routing Prefix is the network portion assigned to a customer or site by a provider and varies based on ISP policies.
• Subnet ID is between the Global Routing Prefix and the Interface ID, and subnets an organization's site.
• The IPv6 Interface ID is the host portion of an IPv4 address and using /64 subnets allows to create a 64-bit interface ID.
• IPv6 allows all-0s and all-1s host addresses assignment; the all-0s address is reserved as a Subnet-Router anycast address for routers only.

IPv6 Link-Local Address

• IPv6 link-local address (LLA) use enables a device to communicate with other IPv6-enabled devices on the same link (subnet).
• Packets with an LLA source/destination cannot be routed.
• Every IPv6-enabled network interface has an LLA.
• A device automatically creates an LLA if not manually configured.
• IPv6 LLAs are in the fe80::/10 range.

Static Configuration

• Static GUA Configuration is similar for both routers and Windows hosts.

Router Configuration

• To configure an IPv6 GUA on an interface: ipv6 address ipv6-address/prefix-length is used.

Windows Host Configuration

• The Global Unicast Address or Link Local Address of the router interface can be used as the default gateway.
• LLA is generally recommended.
• DHCPv6 or SLAAC automatically specify the routers LLA as the default gateway address.

Static LLA configuration

• Manual interface configuration is preferable for recognizable and memorable addresses.
• LLAs configured using ipv6 address ipv6-link-local-address link-local command.
• Same LAN LLA must be unique though the same LLA can be used on multiple links.
• Different LLA can made on each router interface to make it easy to identify the router and specific interface.

Dynamic Addressing for IPv6 GUAs

• Devices dynamically obtain GUAs through Internet Control Message Protocol version 6 (ICMPv6) messages.
• Router Solicitation (RS) messages are sent by hosts to discover IPv6 routers.
• Router Advertisement (RA) messages are sent by routers providing hosts network information such as:
  • Network prefix and prefix length
  • Default gateway address
  • DNS addresses and domain name
  • Methods for configuring IPv6 GUA (SLAAC,SLAAC with stateless DHCPv6 server, Stateful DHCPv6 (no SLAAC).

SLAAC Addressing

• SLAAC allows to configure a GUA without DHCPv6.
• Necessary information configures a GUA from ICMPv6 RA messages.
• The prefix is provided by the RA and either the EUI-64 or the random generation method creates an interface ID.

SLAAC and Stateless DHCP Addressing

• An RA instructs a device to use both SLAAC and stateless DHCPv6 by:
  • Creating its own IPv6 GUA using SLAAC
  • The router LLA sets the RA source IPv6 address.
  • Using a stateless DHCPv6 server to obtain other information like a DNS server address or a domain name.

Stateful DHCPv6 Addressing

• RA instructs a device to use stateful DHCPv6 (similar to IPv4 DHCP).
• A device can automatically receives a GUA, prefix length, and DNS servers address via a stateful DHCPv6 server.
• It uses the router LLA, which comes from the RA source IPv6 address, for the default gateway address.
• A stateful DHCPv6 server is used to obtain a GUA, DNS server address, domain name and other info.

EUI-64 Process vs. Randomly Generated

• When RA is SLAAC or SLAAC with stateless DHCPv6, the client generates its own Interface ID.
• The Interface ID can be created using the EUI-64 process or a randomly generated 64-bit number.

EUI-64 Process

• The IEEE defined the Modified EUI-64 process which:
  • Inserts a 16-bit value of fffe (hexadecimal) into the middle of the client's 48-bit Ethernet MAC address.
  • Reverses the 7th bit of the client MAC address from binary 0 to 1.

Randomly Generated Interface IDs

• A device's operating system uses a randomly generated interface ID, instead of the MAC address and the EUI-64 process.
• Windows uses a random interface ID over EUI-64 since Windows Vista.
• Duplicate Address Detection (DAD) ensures uniqueness of an IPv6 unicast address, similar to ARP.

Dynamic LLAs

• All IPv6 interfaces have to have an IPv6 LLA.
• LLAs, like IPv6 GUAs, can be configured dynamically.
• A dynamically created LLA utilizes the fe80::/10 prefix and interface ID using the EUI-64 process or generated 64-bit number.

Dynamic LLAs on Windows

• Windows uses the same method for a SLAAC-created GUA and dynamically assigned LLA.

Dynamic LLAs on Cisco Routers

• Cisco routers automatically create an IPv6 LLA when a GUA is assigned.
• Cisco IOS routers will use EUI-64 to generate interface ID for all LLAs on IPv6 interfaces by default.

Assigned IPv6 Multicast Addresses

• IPv6 multicast addresses use a prefix ff00::/8.
• They include Well-Known and Solicited node multicast addresses.
• Multicast addresses can only be destination addresses.

Well-Known IPv6 Multicast Addresses

• Well-known IPv6 multicast addresses are assigned and reserved for predefined groups of devices.
• Assigned multicast groups that include.

All-nodes multicast group

• ff02::1 which involves all IPv6-enabled devices join.
• Packets sent to this group are received processed by all IPv6 interfaces on the link or network.

All-routers multicast group

• ff02::2 which involves all IPv6 routers join.
• A router joins it once IPv6 is enabled and configured with the ipv6 unicast-routing global command.

Solicited-Node IPv6 Multicast

• The device can filter the frame.
• It examines the destination MAC address.
• This is done without sending it to IPv6 process, meaning it determines if the device is the intended target of a IPv6 packet.

##IPv6 Neighbour Discovery

IPv6 ND Msgs

• It allows IPv6 to send control messages (like IPv4). Message types are as below:
• Echo request
• Echo reply,
• Destn Unreachable
• Router discovery

ICMPv6 features:

• It offers additional features like NDP(Neighbour discovery protocol)
• NDP: Is a set if ICMPv6 messages which will allow IPv6 terminals to complete below tasks:

1. Auto configure IPv6 address
2. Discover MAC address of neighbours.

• NDP is successor to ARP, as it helps discover MAC addresses

ICMPv6 msgs for NDP

• There are in total 4 ICMPv6 msgs for NDP

Router advertisement

• RA: It is covered in chapters to come and discussed further

Router solicitation:

• RS: It is covered in chapters to come and discussed further
• ICMPv6 Neighbor Solicitation and Neighbor Advertisement
• msgs are used for device-to-device messaging.
• Such as Address resolution (ARP)

ND - Address resolution

• IPv6 devices will help ND to resolve MAC address in a known IPv6 address
• It will allow ICMPv6 Neighbour solicitation msgs to get sent using special Ethernet - IPv6 multicast addresses

Neighbour solicitation advertisement

Exchange utility for MS Address

• Exchange can help determine MAC address of a neighbour
• NS destinations can solicit MS of destn

Utility the solicited MS address

• Can give same address to same host