IPv6 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:

    • Generate interface ID and create link-local address (i.e. EUI-64);

    • Discover prefix on link through Router Advertisement messages;

    • 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


    • 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:

    • 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)

© Robert Larsen. All rights reserved.