What are pros and cons of using expansionary and contractionary fiscal and monetary policy tools?

What are the various ways to access IPv6 over IPv4?  And what are the pros and cons for each method?

• I'm aware of 6to4 and 6RD.  I'm currently using AICCU with SixXS as my tunnel broker, and stuff is sent over AYIYA (http://www.sixxs.net/tools/ayiya/).  I'm aware that MacOS X has a 6to4 option, but after messing around, I haven't the foggiest idea how to get it working or if I can get it working to begin with.  I get the vague feeling that I need a cable modem that supports DOCSIS 3.0, a router that'll forward protocol-41 or something like that. (As for they "Why do you want IPv6?" that some people might be asking, well... I just do. It's new and shiny and I want to play with it.)

• Answer:

  Your best bet is to avoid tunneling altogether and seek out a native IPv6 Internet Service Provider.  This will be much easier after World IPv6 Launch (http://www.worldipv6launch.org) on June 6, 2012. That said, the most popular methods of tunneling IPv6 packets inside IPv4 are 6rd, 6to4, 6in4, AYIYA, and Teredo. 6rd is a MANAGED TUNNEL.  Using the IPv6 prefix of the 6rd headend plus additional prefix bits derived from the IPv4 address, a central tunnel headend acts as an exit and entry point for the IPv6 traffic over the managed tunnel, providing an IPv6 prefix to the serviced network (e.g., a home network).  The trick with 6rd is that the gateway to the serviced network needs to learn its prefix and prefix length, the IPv4 address of the 6rd headend and the number of prefix bits.  These can be learned by a service provider managed method (like DHCP) or manually entered.  The actual IPv6 traffic is encapsulated in IPv4 protocol 41. 6to4 is an UNMANAGED TUNNEL.  No configuration is required, but the device originating the tunnel MUST have a globally routable address, not an RFC 1918 private address.  6to4 uses a reserved IPv6 prefix for addressing (2002::/16) and a well-known IPv4 anycast address to locate the nearest headend (192.0.2.42).  Traffic flows asymmetrically; your packet will transition to the IPv6 network at the nearest 6to4 gateway, and the return traffic will transition back top the IPv4 network at the 6to4 gateway nearest the IPv6 destination. 6to4 relies on the kindness of strangers to route the packet, and neither the performance nor routing path of the traffic can be well predicted in this environment.  Read "Unmanaged Tunnels Considered Harmful" for a full treatise on the subject. The actual IPv6 traffic is encapsulated in IPv4 protocol 41. In your 6to4 case, you probably could not get 6to4 working because your Mac had an RFC 1918 address.  Generally, a device will not try to open a 6to4 tunnel if your IPv4 address is an RFC 1918 address.  Even if the tunnel were to be opened, the IPv6 address would be assigned incorporating the RFC 1918 address as part of the IPv6 address.  As a result, the traffic would be encapsulated in IPv4 and sent to the 6to4 outbound gateway and in turn on to the IPv6 host.  When the IPv6 host replies, his nearby 6to4 gateway will extract the RFC 1918 address embedded the IPv6  address and drop the packet since the extracted IPv4 address is not globally routable. 6in4 is a MANUALLY CONFIGURED TUNNEL, like what http://tunnelbroker.net uses.  The IPv6 addresses of the local end of the tunnel and the network interface  need to be manually configured, as does the IPv4 address of the tunnel headend.  The IPv6 traffic actual traffic is encapsulated in IPv4 protocol 41. The three IPv4 protocol 41 techniques listed above are generally not NAT /NAPT friendly, since NAT relies on the use of some non-address hook (like a TCP or UDP port) to demultiplex traffic to multiple devices sharing a single IPv4 address, AYIYA is a mechanism to carry IPv6 in UCP, TCP or SCTP packets, allowing tunnels to flow through NAT devices.  SiXXS uses this. AICCU is a control mechanism to allow dynamic setup of 6in4 or AYIYA tunnels.    SiXXS uses this. TSP (Tunnel Setup Protocol) is another control mechanism for tunnel setup.   It also provides a mechanism to tunnel IPv6 over UDP on port 3653.  Gogonet uses this. Teredo is Microsoft's IPv6 tunneling technique which touts NAT friendliness due to its use of UDP to encapsulate IPv6 packets.  In practice, Teredo is rarely used for IPv6 connectivity since it tends to rely on a very small number of highly overloaded public IPv4 to IPv6 relays and suffers from a number of serious design flaws that limit its usefulness.  As a side note, you many find some enterprise networks using ISATAP. Enterprises can set up a collection of internal IPv4 to IPv6 routers which hand out IPv6 addresses to IPv4 devices which reach out to a well known IPv4 address (http://ISATAP.domain.com).  The actual IPv6 traffic is encapsulated in IPv4 protocol 41. Unfortunately, ISATAP only appears on Windows some *nix flavors.  No support can be found in MacOS, iOS, or most mobile devices. What tunneling protocol do I recommend?  NONE!  The time for tunneling is long past. Insist that your ISP provide native IPv6 connectivity.  It's time.  Refer to http://www.worldipv6launch.org to find participating providers, and vote with your wallet.