IPv6 Addressing Formats

IPv6 Unicast Addresses

• IPv6 devices typically have two unicast addresses: Global Unicast Address (GUA) and Link-local Address (LLA)
• Global Unicast Address (GUA) is similar to a public IPv4 address, globally unique, and internet-routable
• Link-local Address (LLA) is required for every IPv6-enabled device, used to communicate with other devices on the same local link, and not routable

IPv6 Global Unicast Address (GUA)

• Global Routing Prefix: the prefix or network portion of the address assigned by the provider
• Subnet ID: the area between the Global Routing Prefix and the Interface ID
• Interface ID: equivalent to the host portion of an IPv4 address
• Command to configure an IPv6 GUA on an interface: ipv6 address/prefix-length

IPv6 Link-local Address (LLA)

• Enables a device to communicate with other IPv6-enabled devices on the same link
• Packets with a source or destination LLA cannot be routed
• Every IPv6-enabled network interface must have an LLA

Dynamic Addressing for IPv6 GUAs

• RS and RA Messages: used to configure IPv6 GUAs
  • Router Solicitation (RS): messages sent by host devices to discover IPv6 routers
  • Router Advertisement (RA): messages sent by routers to inform hosts on how to obtain an IPv6 GUA
• RA provides useful network information, including:
  • Network prefix and prefix length
  • Default gateway address
  • DNS addresses and domain name
• Three methods to configure an IPv6 GUA:
  • SLAAC (Stateless Address Autoconfiguration)
  • SLAAC with stateless DHCPv6 server
  • Stateful DHCPv6

SLAAC (Stateless Address Autoconfiguration)

• Allows a device to configure a GUA without the services of DHCPv6
• Device uses either the EUI-64 or random generation method to create an Interface ID
• Prefix is provided by the RA

SLAAC with Stateless DHCPv6

• RA suggests devices use SLAAC to create its own IPv6 GUA
• RA suggests devices use a stateless DHCPv6 server to obtain other information
• Device uses the router LLA as the default gateway address

Stateful DHCPv6

• RA instructs a device to use stateful DHCPv6 only
• Device can receive:
  • Automatically configured GUA
  • Prefix length
  • The addresses of DNS servers from a stateful DHCPv6 server

EUI-64 Process

• Extended Unique Identifier (EUI) or modified EUI-64 process
• Inserts a 16-bit value of fffe (in hexadecimal) into the middle of the 48-bit Ethernet MAC address of the client

IPv6 Multicast Addresses

• Prefix: ff00::/8
• Used to send a single IPv6 packet to multiple destinations

TCP Reliability

• Data Loss and Retransmission: retransmit segments for unacknowledged data
• TCP Flow Control: adjusts the rate of data flow between source and destination for a given session
• Maximum Segment Size (MSS): the maximum amount of data that the destination device can receive
• Congestion Avoidance: uses timers and algorithms to avoid and control congestion

UDP

• Does not establish a connection
• Provides low overhead data transport due to small datagram header and no network management traffic
• Does not track sequence numbers or reorder datagrams into their transmission order

Domain Name Service (DNS)

• Converts numeric IP addresses into a simple, recognizable name
• FQDNs (Fully-Qualified Domain Names): used to identify a domain name, e.g. http://www.cisco.com
• DNS protocol: defines an automated service that matches resource names with the required numeric network address
• DNS server stores different types of resource records, including:
  • A: an end device IPv4 address
  • NS: an authoritative name server
  • AAAA: an end device IPv6 address
  • MX: a mail exchange record

DNS Message Format

• DNS uses a hierarchical system to create a database to provide name resolution
• Database file is only responsible for managing name-to-IP mappings

IPv6 Addressing Formats

• IPv6 addresses are 128 bits in length, written in hexadecimal
• Preferred format: x:x:x:x:x:x:x:x (each "x" consisting of four hexadecimal values)
• Example: 2001:0db8:0000:00a3:abcd:0000:0000:1234

IPv6 Address Representation Rules

• Rule 1: omit leading zeros
• Rule 2: use a double colon (::) to replace any single, contiguous string of one or more 16-bit hextets consisting of all zeros

IPv6 Address Types

• Three broad categories: Unicast, Multicast, and Anycast
• Unicast: uniquely identifies an interface on an IPv6-enabled device
• Multicast: used to send a single IPv6 packet to multiple destinations
• Anycast: can be assigned to multiple devices, packet routed to the nearest device having that address

IPv6 Prefix Length

• Represented in slash notation and used to indicate the network portion of an IPv6 address
• Recommended IPv6 prefix length for LANs and other types of networks is /64