Technical


  • Router Discovery: used since there is no default gateway configuration:
    • Every host must discover a router by sending out "Router Solicitation" messages.
    • Routers will respond with a "Solicited Router Advertisement".
    • Routers will also send out "Router Advertisements" at regular intervals.
    • Router advertisements contain:
      • The link-local address of the router;
      • Info about the link (e.g. default hop limit);
      • Router lifetime;
      • What addresses exist on this link (e.g. global or ULA).
  • SLAAC: StateLess Auto Address Configuration:
    1. Generate interface ID and create link-local address (i.e. EUI-64);
    2. Discover prefix on link through Router Advertisement messages;
    3. Verify address uniqueness (DAD: Duplicate Address Detection).
  • DHCPv6: is not mandatory:
    • Stateful DHCPv6 keeps state of client address leases;
    • Provides additional information (e.g. DNS server, domain, etc.);
    • Similar to IPv4 DHCP (some message types have changed);
    • Stateful DHCPv6 is not commonly available in IPv6 stacks.
  • Address Resolution: IPv6 neighbour discovery:
    • Send out "Neighbour Solicitation" message.
    • Receive "Neighbour Advertisement" reply.
  • Transition Phases:
    • Phase 1 - Early Adopters: IPv6 in IPv4 tunnelling from the home.
    • Phase 2 - Distributed IPv6 over Ethernet for unicast services.
    • Phase 3 - IPv6 over Ethernet for unicast and multicast services.
  • NAT444: (LSN - Large Scale NAT)
Private IPv4 <-NAT44-> Private IPv4 <-NAT44-> IPv4 Internet
 Home N/W               Access N/W   Stateful
    • No change required to CPE.
    • Have to be careful of:
      • Address overlaps between customer's RFC1918 addresses and the provider-assigned RFC1918 addresses.
      • Routing between end subscribers -- can use:
        • Hairpinning.
        • SP shared addresses.
  • NAT 64 + DNS64:
IPv6  <-->  IPv6  <-NAT64->  IPv4 Internet
Home       Access  Stateful
  • NAT464:
Private IPv4  <-NAT46->    IPv6    <-NAT64-> IPv4 Internet
  Home N/W    Stateful  Access N/W  Stateful
    • Is closer to a pure IPv6 network than NAT444.
    • Eases the burden of having to assign and manage both IPv4 and IPv6 addresses on links.
    • Because of translation between IPv4 and IPv6 address families:
      • Is more complex than NAT444.
      • Doesn't perform or scale as well as NAT444.
  • DS Lite: (Dual Stack Lite)
Private IPv4   <--+     
                  |     
Private IPv4   <--+-->    <-NAT44->  IPv4 Internet
                  |     
Private IPv4   <--+     
  Home N/W    Access N/W
               Tunnels  
    • Uses IPv6-only links between the customer and the provider.
    • Tunnels IPv4 traffic over IPv6.
    • The LSN performing the NAT44 has to also track the source address of the encapsulating IPv6 packet.
    • Disadvantage is that CPE needs to be upgraded (either software or hardware), but may not be a big problem:
      • It is new customers who are creating demand for new IP addresses.
      • Existing customers can be upgraded as part of normal hardware refresh or churn cycles.
    • DS Lite can also run in the protocol stack on an individual end system -- useful for:
      • Single PC, laptop, gaming systems connected to the Internet.
      • Mobile broadband.
  • NAT type comparison:
FeatureNAT444NAT64 + DNS64NAT464DS Lite
 Customer PremiseNo CPE changeHost must support IPv6CPE changeCPE change
DisadvantagePotential overlapping address space between CPE and LSNOnly supports IPv6 hosts (WinXP does not support DNS64)IPv4 translated into IPv6IPv4 is tunneled over IPv6
Traffic BypassApplication servers can sit between subscriber and LSNAll IPv4 traffic must be subject to NAPTAll IPv4 traffic must be subject to NAPTAll IPv4 traffic must be subject to NAPT
Current BNG/BRASMinimal impactTunnel obfuscates all IPv4 trafficTunnel obfuscates all IPv4 trafficTunnel obfuscates all IPv4 traffic
  • Dual Stack: The only real problem with this is how can you dual stack if you've run out of IPv4 addresses?
    • Therefore: must start to dual stack before running out of IPv4 addresses.
  • Migration Options:
    • Dual stack: network runs both stacks, effectively "ships in the night".
    • 6over4: IPv6 tunneled over an IPv4 backbone.
    • 6PE: IPv6 tunneled over an IPv4/MPLS backbone.
    • 6VPE: same as 6PE, but additionally supports multiple VRFs on the PE routers.
    • DS-Lite.
    • 6RD.
    • NAT64/DNS64.

Various IPv6-Related RFCs

  • RFC5569: IPv6 Rapid Deployment on IPv4 Infrastructures (6rd)