6to4-Derived Addressing (IPv6 Administration Guide)

IPv6 Administration Guide

6to4-Derived Addressing

As with native IPv6 routers, you must advertise the subnet prefixes derived from the site 6to4 prefix in /etc/inet/ndpd.conf. The next figure shows the parts of a prefix for a 6to4 site, as described in 6to4 Prefix Format and 6to4 Advertisement Example.

Figure 4–4 Parts of a Site Prefix

This figure shows the format of a 6to4 site prefix and shows a site prefix example. The cited tables explain the information in the figure.

The next figure shows the parts of a subnet prefix for a 6to4 site, such as you would include in the ndpd.conf file.

Figure 4–5 Parts of a Subnet Prefix

This figure shows the format of a 6to4 prefix and shows a prefix example. The following context explains the information in the figure.

6to4 Prefix Format

The format line in the previous figure contains the following parts.

Part	Length	Definition
Prefix	16 bits	6to4 prefix 2002 (0x2002).
IPv4 address	32 bits	Unique IPv4 address that is already configured on the 6to4 interface. For the advertisement, you specify the hexadecimal representation of the IPv4 address, rather than the IPv4 dotted–decimal representation.
Subnet ID	16 bits	Subnet ID, which must be a value that is unique for the link at your 6to4 site.

6to4 Advertisement Example

The example in the previous figure has the following values.

Advertisement Part	Corresponding Value
6to4 prefix	2002
IPv4 address	8192:56bb, which corresponds to IPv4 address 129.146.87.188
Subnet ID	1
/64	Length of prefix

6to4-Derived Addressing on a Host

When an IPv6 host receives the 6to4–derived prefix by way of a router advertisement, the host automatically reconfigures a 6to4–derived address on an interface. The address has the following form.

prefix:IPv4 address:subnet ID:host ID/64

The results of ifconfig –a on a host with a 6to4 interface might resemble the following:

qfe1:3: flags=2180841<UP,RUNNING,MULTICAST,ADDRCONF,ROUTER,IPv6>
 mtu 1500 index 7
        inet6 2002:8192:56bb:9258:a00:20ff:fea9:4521/64

The 6to4–derived address follows inet6 in the output from ifconfig.

Address Part	Corresponding Value
`Prefix`	2002, which is the 6to4 prefix
`IPv4 value`	8192:56bb, which is the IPv4 address, in hexadecimal notation, for the 6to4 pseudo-interface that is configured on the 6to4 router
subnet ID	9258, which is the address of the subnet of which this host is a member
MAC address	a00:20ff:fea9:4521, which is the link layer address of the host interface that is now configured for 6to4