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Lecture 5 - IPv6
Alejandro Saucedo - Comp2008 Lecture 5 FlashCard Set
Computer Networking
Undergraduate 2

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What are some reasons why IPv6 was deployed?
  • Exhaustion of IPv4 address space
  • Enabling end-to-end global addressing
  • Securing IPv6 in your own "IPv4 only" network
  • Simplify ability for early adopter-only access networks to reach your content
  • New applciations: sensors, logistics, transport, etc
What are the Benefits of IPv6
  • Architectural
    • 128-bit addresses
    • Support for billions more devices online
    • Potential to restore end-to-end capability
    • Removal of the need for NAT
  • Technical
    • Network (IP configuration) plug and play
      • Stateless Address Autoconfiguration
    • Steamlined, extensible IPv6 header
    • Fragmentation only at sender
Draw a diagram the IPv6 header
What are the benefits of IPv6 over IPv4 headers?
  • Less fields, with a fixed header size
  • Concept of a chain of headers
    • One header per function e.g:
      • Authentication header
      • Fragmentation header
    • The 'next header' field links headers together
    • In theory, one cen define new headers
      • In practice, tricky due to firewall considerations
What are the features of IPv6 addressing?
  • Unicast: one to one
  • Multicast: one to many
  • New. Various scopes of addresses are defined
    • Link-local addresses - used only on local subnets
      • Uses prefix fc00::/7
      • Global addresses - globally unique and routable
What are Unique Local Addresses (ULA)?
  • An IPv6 address in the block fc00::/7.
  • Approximate counterpart of the IPv4 private address
  • Not accessible in the global IPv6 Internet
  • In IPv6 hosts may routiney be multi-addressed
    • One or more global IPv6 address(es)
    • One IPv6 link-local address
    • Possibly a ULA
Does IPv6 implement NAT?
  • IPv6 has enough address space not to require Network address translation purely for address conservation
  • MIght still be implemented for 'Security benefits'
  • Using ULAs doesn't imply you have to use IPv6 NAT
  • If hosts have global address from ISP and ULA:
    • They can use their ULA to talk internally
    • Can use their global address to talk externally
    • If they change ISP, and their global address has to change, the use of ULAs keeps internal communications stable
What are host configuration tools?
  • For both IPv4 or IPv6
    • An IP address to use
    • The size of the local subnet (prefix size)
    • The default router to use on the local subnet
    • DNS server(s)/resolver(s) to use
  • In IPv4 you can use
    • Manual configuration (Typically for servers)
    • or Dynamic Host Configuration Protocol (DHCP)
What are the principles of Stateless Address Autoconfiguration (SLAAC)
  • IPv6 hosts can also autoconfigure basic network settings without the need for a stateful DHCP server
    • IP address
    • Default gateway
  • An IPv6 Host using SLAAC by default builds its address from:
    • An advertised 64-bit(/64) network prefix
    • A 64-bit host part generated based on MAC
  • Prefix information is advertised by a router, either
    • Periodically (Typically every 600 seconds)
    • Request (node sends Router Solicitation request)
    • The Advertisement is multicast on the local subnet
What are the characteristics of an IPv6 Router Advertisement?

Host sees or solicits a RA from router - the response includes:

  • RA message carries the network prefix to use
  • RA (link-local) source address implies default router
  • RA can indicate if a DHCPv6 service is available
  • DNS server information can be included in RA
Give an example of an IPv6 autoconf
  • Host's Ethernet (MAC) address is 08:00:20:9c:14:66
  • The network prefix in the RA is 2001:630:80:200::/64
  • Address is 2001:630:80:200:0a00:20ff:fe9c:1466
    • A MAC address is 48 bits, ehnce the fffe 16-bit padding
    • the "0a" is the globally unique EUI-64 bit being set


What are some IPv6 privacy issues and extensions?
  • MAC address is being embeded in the autoconfigured IPv6 address
  • If device moves between networks, its prefix changes but the 64-bit identifier part remains the same
  • Device can be tracked over time
  • Privacy extensions instead use a random host part
    • Generated when device joins network - and changes over time
    • Also applies to static hosts - generates new privacy address periodically
    • Increases complexity
What are the main functions of IPv6 Neighbour Discovery?
  • Router Advertisements
  • Neighbour solicitation/advertisements¬†
    • Similar to ARP
What are some characteristics of port-scanning resilience of IPv6?
  • Post-scanning is common in IPv4
  • In IPv4 one port per subnet is 5 minutes (256 addresses)
  • In IPv6 it is 500 billion years (2^64 hosts per subnet)
  • There are ways to narrow search space
  • 'Security through obscurity'
What are dual-stack subnets?
Hosts that have both an IPv6 and IPv4 address
What are the approaches to introduce IPv6?
  • Dual Stack
  • Translation Methods (IPv4-only to IPv6-only)
    • Rewriting IP header information
    • Application layer gateways (ALGs)
  • Tunnels
    • IPv6 traffic encapsulated in IPv4 packets
    • router-to-router or host-to-router
What are the main characteristics of Dual Stack Systems?
  • Run both protocols on same equipment
  • May need to rewrite/port existing applications
  • Need to choose when to use IPv4 or IPv6
  • Assumes enough IPv4 addresses are available
  • Need to secure both protocols
What is tunnelling between sites?

Encapsulate IPv6 packet as payload/data of an IPv4 packet, usually manually configured on two routers


IPv4 packets carry IPv6 packets as their data

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