298Understanding IPv6, Second Edition

Table 13-1 Example 6to4 Addresses

Because 6to4 addresses are always global, you do not need %ZoneID as part of the destination address.

The 6to4 tunneling interface uses its own 6to4 address as a source IPv6 address. The 6to4 tunneling interface determines the destination IPv4 address of the encapsulating IPv4 header from the second and third blocks of the destination IPv6 address (the first 32 bits after 2002::/16), which correspond to the embedded IPv4 address of Host B. For the source IPv4 address in the encapsulating IPv4 header, IPv4 on Host A determines the best source IPv4 address to use to reach the destination IPv4 address 157.54.0.1. In this case, Host A has only a single IPv4 address assigned, so IPv4 on Host A uses the source address of 131.107.0.1.

6to4 Components

A 6to4 deployment consists of 6to4 hosts, 6to4 routers, 6to4 host/routers, and 6to4 relays. Figure 13-3 shows the components of 6to4 and their placement on the IPv4 and IPv6 Internets.

The 6to4 components shown in Figure 13-3 are the following:

■6to4 host A native IPv6 host that is configured with at least one 6to4 address (a global address with the 2002::/16 prefix). 6to4 hosts do not require any additional support or manual configuration and can create 6to4 addresses using standard address autoconfiguration mechanisms. 6to4 hosts do not have a 6to4 tunneling interface and do not perform 6to4 tunneling.

■6to4 router An IPv6/IPv4 router that uses a 6to4 tunneling interface to forward 6to4addressed traffic between the 6to4 hosts within a site and other 6to4 routers, 6to4 host/ routers, or 6to4 relays across the IPv4 Internet. 6to4 routers might require manual configuration.

■6to4 host/router An IPv6/IPv4 host that uses a 6to4 tunneling interface to exchange 6to4-addressed traffic with other 6to4 host/routers, 6to4 routers, or 6to4 relays across the IPv4 Internet. Unlike a 6to4 router, a 6to4 host/router does not forward traffic for other 6to4 hosts. An example of a 6to4 host/router is a computer running Windows Vista that is directly connected to the Internet and has been assigned a public IPv4 address.

■6to4 relay An IPv6/IPv4 router that forwards 6to4-addressed traffic between 6to4 routers and 6to4 host/routers on the IPv4 Internet and hosts on the IPv6 Internet. Microsoft has deployed a 6to4 relay on the IPv4 Internet, which is reachable by resolving the Domain Name System (DNS) name 6to4.ipv6.microsoft.com to an IPv4 address. RFC 3068 also defines an IPv4 anycast prefix for 6to4 relays.

IPv6 over IPv4 Traffic

IPv6 Traffic

6to4 Host

Figure 13-3 6to4 components on the IPv4 and IPv6 Internets

Note RFC 3056 uses the term “relay router” for the 6to4 relay. This chapter uses the term “6to4 relay” to better distinguish a 6to4 relay from other types of IPv6 transition relays between the IPv4 Internet and IPv6 Internet.

Both the 6to4 host/router and the intranet connected to the 6to4 router are 6to4 sites, which are hosts or networks connected to the IPv4 Internet that have their own unique 2002:WWXX:YYZZ::/48 prefix. For the 6to4 host/router the entire 6to4 site consists of a single computer. For the 6to4 router, the entire intranet is a 6to4 site, which can consist of up to 65,636 IPv6 subnets (using all possible combinations of the 16-bit Subnet ID). A 6to4 site can be created from every public IPv4 address.

Within a 6to4 site connected to the IPv4 Internet with a 6to4 router, IPv6 routers advertise 2002:WWXX:YYZZ:SubnetID::/64 prefixes so that 6to4 hosts can create an autoconfigured 6to4 address.