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

               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:

• • 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.