Notice that the Router Advertisement message contains an MTU option setting the maximum transmission unit (MTU) over the tunnel interface to 1280 and two Prefix Information options—one for the global prefix 2001:DB8:3C5A:21DA::/64, and one for the unique local prefix FD31:2C00:8D33:21DA::/64.

Using the netsh interface isatap set router Command

Although automatic configuration of the IPv4 address of the ISATAP router through the resolution of the name “ISATAP” is the recommended method to use, you can manually configure the IPv4 address of the ISATAP router with the netsh interface isatap set router command. The syntax of this command is

netsh interface isatap set router AddressOrName

AddressOrName is the name or IPv4 address of the ISATAP router’s interface on the ISATAP subnet. If you use a name, the name must be resolvable to the IPv4 address of the ISATAP router. An address is recommended over a name.

For example, if the ISATAP router’s IPv4 address on the ISATAP subnet is 192.168.39.1, the command is

netsh interface isatap set router 192.168.39.1

Note Computers running Windows Server 2008 or Windows Vista support Netsh commands for configuring ISATAP behavior in both the netsh interface isatap and netsh interface ipv6 isatap contexts. Computers running Windows Server 2003 or Windows XP support only the netsh interface ipv6 isatap context. This chapter uses the ISATAP commands in the netsh interface isatap context.

ISATAP Addressing Example

Figure 12-4 shows an ISATAP addressing example.

In this configuration, the ISATAP router is advertising the global subnet prefix 2001:DB8:0:7::/64 to the ISATAP hosts on the ISATAP subnet. ISATAP Host A, configured with the IPv4 address 192.168.47.99, uses the subnet prefix advertised by the ISATAP router to automatically configure the global ISATAP address of 2001:DB8::7:0:5EFE:192.168.47.99. Host A attempts to register the IPv6 address record (AAAA) for the address 2001:DB8::7:0:5EFE:192.168.47.99 in DNS.

Similarly, ISATAP Host B uses the subnet prefix to automatically configure the global ISATAP address of 2001:DB8::7:200:5EFE:131.107.71.209. Host B attempts to register the IPv6 address record (AAAA) for the address 2001:DB8::7:200:5EFE:131.107.71.209 in DNS.