Chapter 12 ISATAP 285 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 reso- lution 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
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286 Understanding IPv6,Second Edition Example Prefix:2001:DB8:0:7::/64 10.0.0.1 ISATAP Router IPv4-Only IPv6-Capable ISATAP Host B 192.168.47.99 131.107.71.209 2001:DB8:0:7:05EFE:192.168.47.99 2001:DB8:0:7:200:5EFE:131107.71.209 ISATAP Host A ISATAP Interface ID::0:5EFE:w.x.y.z or ::200:5EFE:w.x.y.z Figure 12-4 ISATAP addressing example ISATAP Routing Figure 12-5 shows the relevant routes for ISATAP communication for the example configura- tion shown in Figure 12-4. Example Prefix:2001:DB8:0:7::/64 10.0.0.1 ISATAP Router IPv6-Capable IPv4-Only Routes: 2001:DB8:0:7:/64to Routes: ISATAP Router ISATAP Host 2001:DB8:0:7:/64On-Link Routes: Through the ISATAP Interface 2001:DB8:0:7::/64 On-Link Through ::/0 to the IPv6-Capable Network Through the ISATAP Interface the LAN Interface ::/0 to FE80::5EFE:10.0.0.1 Through the ISATAP Interface Routes: 2001:DB8:0:7:/64 On-Link Through the ISATAP Interface ::/0 to FE80::5EFE:10.0.0.1 Through the ISATAP Interface ISATAP Host Figure 12-5 ISATAP routing example
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Chapter 12 ISATAP 287 ISATAP hosts use the following routes: An on-link route for the ISATAP subnet prefix that uses the ISATAP tunneling interface. This route allows ISATAP hosts to perform host-to-host tunneling to reach other ISATAP hosts on the same ISATAP subnet.In the example configuration,this is the 2001:DB8:0:7:/64 route. A default route with the next-hop address of the ISATAP router's link-local ISATAP address(FE80::5EFE:10.0.0.1)that uses the ISATAP tunneling interface.This route allows ISATAP hosts to perform host-to-router tunneling to reach the IPv6 hosts on the IPv6-capable portion of the intranet. An ISATAP router uses the following routes: An on-link route for the ISATAP subnet prefix that uses the ISATAP tunneling interface that is associated with the LAN interface that is connected to the ISATAP subnet.This route allows the ISATAP router to perform router-to-host tunneling to reach other ISATAP hosts on the ISATAP subnet.In the example configuration,this is the 2001:DB8:0:7:/64 route. A default route that uses a LAN interface that is connected to the IPv6-capable portion of the intranet and has the next-hop address of a neighboring router(not shown in Figure 12-5).This route allows the ISATAP router to forward IPv6 traffic to destinations on the IPv6-capable portion of the intranet. The routers of the IPv6-capable network use a route for the ISATAP subnet prefix that points back to the ISATAP router.This route allows the routers of the IPv6-capable network to for- ward traffic destined for the ISATAP hosts on the ISATAP subnet to the ISATAP router.In the example configuration,this is the 2001:DB8:0:7::/64 route. ISATAP Communication Examples The following sections describe how ISATAP communication works for the following types of communication: An ISATAP host sends a packet to an ISATAP host on the same ISATAP subnet. An ISATAP host sends a packet to an IPv6 host that is on an IPv6-capable subnet. ISATAP Host to ISATAP Host Figure 12-6 shows how an ISATAP host communicates with another ISATAP host on the same ISATAP subnet for the example configuration of Figure 12-4. In this example,ISATAP Host A has resolved ISATAP Host B's global ISATAP address through a DNS name query and is sending ISATAP Host B a packet.When sending the packet,IPv6 on ISATAP Host A performs the IPv6 route determination process and finds that the closest
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288 Understanding IPv6,Second Edition matching route to the destination is the 2001:DB8:0:7::/64 route for the on-link ISATAP sub- net.Because it is an on-link route.the next-hop IPv6 address for the packet is set to the desti nation address (2001:DB8:7:200:5EFE:131.107.71.209).IPv6 on ISATAP Host A hands the IPv6 packet and the next-hop address to the ISATAP tunneling interface for processing. Example Prefix:2001:DB8:0:7::/64 2001:DB8:0:7:200:5EFE:131.107.71.209 ISATAP Router IPv4-Only IPv6-Capable ISATAP Host B 2001:DB8:0:7:0:5EFE:192.168.47.99 Routes: 2001:DB8:0:7::/64 On-Link Through the ISATAP Interface ::/0 to FE80::5EFE:10.0.0.1 Through the ISATAP Interface ISATAP Host A IPv4 Header Destination Address:131.107.71.209 Source Address:192.168.47.99 IPv6 Header: Destination Address:2001:DB8:0:7:200:5EFE:131.107.71.209 Source Address:2001:DB8:0:7:0:5EFE:192.168.47.99 Figure 12-6 Example of ISATAP host to ISATAP host communication The ISATAP tunneling interface sets the destination IPv4 address in the IPv4 header to the last 32 bits of the next-hop address,which in this case is ISATAP Host B's IPv4 address of 131.107.71.209.IPv4 on ISATAP Host A determines that the best source address to use is the IPv4 address assigned to ISATAP Host A(192.168.47.99),and then IPv4 sends the packet. On ISATAP Host B.IPv4 processes the IPv4 header and,because the Protocol field is set to 41, it hands the encapsulated IPv6 packet to the IPv6 protocol for further processing. ISATAP Host to IPv6 Host When an ISATAP host sends a packet to an IPv6 host on the IPv6-capable network,the packet's journey has two parts: Part 1:From the ISATAP host to the ISATAP router Part 2:From the ISATAP router to the IPv6 host
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