An anycast address is an identifier for a set of interfaces typically belonging to different nodes. Packets sent to an anycast address are delivered to one of the interfaces identified as the "nearest" address, according to the routing protocol's measure of distance.

The format for anycast addresses is identical to the unicast format.

1.2.2.3 Multicast Address

A multicast address is an identifier for a group of nodes. It is similar to an IPv4 multicast address. Figure 1-7 shows the format for multicast addresses.

Figure 1-7 IPv6 Multicast Address

In the multicast address format, the fields have the following definitions:

11..11	Identifies the address as multicast.
Flags	Can be either of the following values: 0000, which indicates a permanently assigned (well-known) multicast address, 0001, which indicates a nonpermanently assigned (transient) multicast address.
Scope	Indicates the scope of the multicast group. The following table lists the scope values: Value (Hex) Scope 1 Node-local 2 Link-local 5 Site-local 8 Organization-local E Global
Group ID	Identifies the multicast group within the specified scope.

Table 1-1 lists some well-known multicast addresses.

Table 1-1 Well-Known Multicast Addresses

Multicast Address	Meaning
FF02::1	All nodes (link-local)
FF02::2	All routers (link-local)
FF02::9	All RIPng routers (link-local)

1.2.3 Address Prefixes

Each IPv6 address has a unique pattern of leading bits that indicates its address type. These leading bits are called the format prefix. Table 1-2 lists some IPv6 address types and their prefixes.

Table 1-2 IPv6 Address Types and Prefixes

Address Type	Prefix
Aggregatable global unicast	2000::/3
Link-local	FE80::/10
Site-local	FEC0::/10
Multicast	FF00::/8

1.2.4 Address Autoconfiguration

The IPv6 address changes have led to the following definitions for configuring addresses:

• Stateless address autoconfiguration
• Dynamic Host Configuration Protocol Version 6 (DHCPv6), which is stateful address autoconfiguration

In the stateless model, nodes learn address prefixes by listening for Router Advertisement packets. Addresses are formed by combining the prefix with a data link-specific interface token, which is typically derived from the data link address of the interface. This model is favored by administrators who do not need tight control over address configuration. See RFC 2462 for more information.

In DHCPv6, hosts may request addresses, configuration information and services from dedicated configuration servers. This model is favored by administrators who want to delegate addresses based on a client/server model. The DHCPv6 Internet Drafts are currently undergoing revision. See the DHCP charter web page for more information:

www.ietf.org/html.charters/dhc-charter.html

In both cases, the resulting addresses have associated lifetimes, and systems must be able to acquire new addresses and release expired addresses. Combined with the ability to register updated address information with Domain Name System (DNS) servers, these mechanisms provide a path towards network renumbering and provide network administrators with control over the use of network addresses without manual intervention on each host on the network.

1.2.5 Address Resolution

The Domain Name System (DNS) provides support for mapping names to IP addresses and mapping IP addresses back to their corresponding names. Because of the increased size of the IPv6 address, the DNS has the following new features:

• AAAA resource record type
  This holds IPv6 addresses, encoded in network byte order. The version of BIND shipped with Compaq TCP/IP Services for OpenVMS supports AAAA records.
• AAAA query
  A query for a specified domain name in the Internet class returns all associated AAAA resource records in the response.
• IP6.INT domain for looking up a name for a specified address (address-to-name mapping)
  An IPv6 address is represented in reverse order as a sequence of 4-bit nibbles separated by dots with the suffix .IP6.INT appended. For example, the IPv6 address 4321:0:1:2:3:4:567:89ab has the following inverse-lookup domain name:

  b.a.9.8.7.6.5.0.4.0.0.0.3.0.0.0.2.0.0.0.1.0.0.0.0.0.0.0.1.2.3.4.IP6.INT

  
  See Chapter 3 for guidelines on configuring BIND in an IPv6 environment.

IPv6 addresses are now being deployed by the regional registries. See the IANA web page at the following location for more information:

http://www.ipv6.org/iana-ann.html

In addition, you can contact your Internet Service Provider (ISP) to obtain an IPv6 address.

Because of the need to test various implementations of the IPv6 RFCs, the IETF has defined a temporary IPv6 address allocation scheme. You can assign the addresses in this scheme to hosts and routers for testing IPv6 on the 6bone (a prototype IPv6 implementation that can be used for testing). See the 6bone home page at the following location for more information about 6bone address allocation and assignment:

http://www.6bone.net

At the present time, the 6bone test addresses are aggregatable global unicast addresses. Contact your 6bone service provider (for example, gw-6bone@pa.dec.com ) for a 6bone address delegation.

The following sections describe the formats for the aggregatable IPv6 addresses.

1.3.1 Aggregatable Global Unicast Addresses

The aggregatable global unicast address format for IPv6 is designed to support current provider-based aggregation and new exchange-based aggregation. Whether a site connects to a provider or to an exchange, the address format enables efficient route aggregation for either type. Figure 1-8 shows the format for an aggregatable global unicast address. (See RFC 2374 for additional information.)

Figure 1-8 Aggregatable Global Unicast Address Format

In this address format, the fields have the following definitions:

Format Prefix	The format prefix. For aggregatable global unicast addresses, the value for this field is 001.
TLA ID	The top-level aggregation identifier.
Reserved	Reserved for future use. At present, set to all zeros (0).
NLA ID	The next-level aggregation identifier. These are assigned by the TLA ID administrator to create an addressing hierarchy and to identify end-user sites. Each organization assigned a TLA ID is also assigned 24 bits of NLA ID space whose layout and use is the responsibility of the organization.
SLA ID	The site-level aggregation identifier. These are used by an individual organization to create its own local addressing hierarchy and to identify subnets.
Interface ID	The 64-bit interface identifier of the interface that is connected to the link.

1.3.2 Aggregatable Testing Addresses

Figure 1-9 shows the format for aggregatable global unicast addresses for IPv6 testing. (See RFC 2471 for more information about the proposed testing address allocation plan.)

Figure 1-9 Aggregatable Testing Address Format

In this address format, the fields have the following definitions:

001	The format prefix for aggregatable global unicast addresses.
1111111111110	The 6bone top-level aggregation (TLA) identifier, 0x1FFE, which is reserved by the Internet Assigned Numbers Naming Authority (IANA) and is used temporarily for IPv6 testing.
pTLA ID	The pseudo top-level aggregation identifier. This is assigned by the pTLA ID administrator to define the top level of aggegation (backbone sites) for the 6bone network.
pNLA ID	The pseudo next-level aggregation identifier. This is the ID assigned by the pTLA ID administrator to create an addressing hierarchy and to identify end-user sites on the 6bone network.
SLA ID	The site-level aggregation identifier. This is the ID assigned by an organization to create its own local addressing hierarchy and to identify subnets.
Interface ID	The 64-bit interface identifier of the interface that is connected to the link.

For the most current information about pTLA and pNLA assignments, see the 6bone home page at the following location:

http://www.6bone.net

1.4 IPv6 Environment

This section shows some example IPv6 configurations. Select a configuration that most closely matches the environment in which you want to configure IPv6 on your system.

Figure 1-10 shows a simple LAN configuration in which host A and host B communicate using IPv6 with no router.

Figure 1-10 Host-to-Host Configuration with No Router

Figure 1-11 shows a simple LAN configuration in which host A, host B, and router A communicate using IPv6. Host A and host B obtain global addresses from router A.

Figure 1-11 Host-to-Host Configuration with Router

Figure 1-12 shows a configuration in which two IPv6 networks are connected through an IPv6 router (router A).

Figure 1-12 IPv6 Network to IPv6 Network with Router Configuration

Figure 1-13 shows a configuration in which four IPv6 networks are connected using three routers. The three routers exchange routing information with each other using the RIPng protocol.

Figure 1-13 Multiple IPv6 Networks and Multiple Routers Configuration

Figure 1-14 shows a configuration in which host A and host B, connected to an IPv4 network, communicate using IPv6 through an IPv4 tunnel.

Figure 1-14 Host-to-Host Configuration over Tunnel

Figure 1-15 shows a configuration in which host X is connected to an IPv4 network. Router A, an IPv6 router, is connected to the same IPv4 network and is also connected to two IPv6 networks. Host X communicates with host B using IPv6 through an IPv4 tunnel between host X and router A.

Figure 1-15 Host-to-Router Configuration over Tunnel

Figure 1-16 shows a configuration in which four IPv6 networks are connected through two routers and an IPv4 network. Host A communicates with host F through an IPv4 tunnel between router A and router B.

Figure 1-16 IPv6 Network-to-IPv6 Network Configuration over Tunnel

After installimg Compaq TCP/IP Services for OpenVMS Version 5.1, you can configure your system to communicate in an IPv6 network environment by performing the tasks described in the following sections. You can configure your node as either of the following:

• IPv6 host
• IPv6 router

Before you configure the network software, you must gather information about your system and network environment. The Configuration Worksheet shown in Figure 2-1 can help you assemble this information in an orderly fashion. The following sections describe the information that you need to record on the worksheet.

Figure 2-1 Configuration Worksheet

1. IPv6 Configuration
   • IPv6 router
     If you want this system to function as an IPv6 router, check Yes; otherwise, check No. If you check No, the system is configured as an IPv6 host.
     An IPv6 router can advertise address prefixes to all hosts on connected links (for example, a LAN and a configured tunnel) and can forward packets to their destinations. Packets can be forwarded directly on link or over IPv4 tunnels.
   • IPv6 interfaces
     Enter the device names of the network interface to the IPv6 network. For example, WE0 and WF0. If you are creating a configured tunnel only on your system, enter None.

   • Configured tunnel
     If you want IPv6 to run over a configured IPv4 tunnel, check Yes; otherwise, check No. A configured tunnel has one source and one destination in an IPv4 network. You should use configured tunnels instead of automatic tunnels. You can configure multiple configured tunnels.
   • Automatic tunnel
     If you want to configure IPv6 to run over IPv4 automatic tunnels, check Yes; otherwise, check No.
   • Manual routes
     If you want to configure manual routes to other systems, check Yes; otherwise, check No.
     On a router, you might want to configure manual routes if one of the following conditions is true:
     • You want a configured tunnel and you are not advertising an address prefix on the tunnel link.
     • You want a configured tunnel and the router at the other end of the tunnel is not running the RIPng protocol.
     • Your system is not running the RIPng protocol.
     
     On a host, you might want to configure manual routes if you want a configured tunnel to a router and the router is not advertising itself as a default router on the tunnel link.
   • Start IPv6
     If you want the IPv6 initialization script executed from the configuration utility, check Yes. If you want the initialization script executed during the next system boot, check No.
2. DNS/BIND
   • Domain name
     The fully qualified domain name for your node. This consists of the host name and the DNS/BIND domain name (for example, host1.subdomain.example ).
3. Configured Tunnel
   • Interface
     The name of the configured tunnel interface. For example, IT0.
   • Destination IPv4 address
     The remote node's IPv4 address (the remote end of the tunnel).
   • Source IPv4 address
     Your node's IPv4 address (this end of the tunnel).
   • RIPng
     If your system is a router and you want the router to run the RIPng protocol on the tunnel link to exchange IPv6 routing information with a router at the remote end of the tunnel, check Yes; otherwise, check No.

   • Address prefix
     If your system is a router and you want to advertise address prefixes to the node at the remote end of the tunnel, enter a 64-bit prefix; otherwise, write Done. If your system is an IPv6 host and the router at the remote end of the tunnel is not advertising an address prefix, enter a 64-bit prefix to be configured on the tunnel interface.
4. Router
   • Interface
     The name of the interface on which you want to run the RIPng protocol or advertise an address prefix.
   • RIPng
     If you want the router to run the RIPng protocol on the specified interface and to exchange IPv6 routing information with other routers on the LAN, check Yes; otherwise, check No.
   • Address prefix
     If you want to advertise address prefixes to all hosts on the link, enter a 64-bit prefix; otherwise, write Done. If you do not specify a 64-bit prefix, the router will not advertise an address prefix. All hosts must obtain their prefix information from another source. Prefixes in IPv6 define a subnet and are typically configured on a router for a specific link by the network administrator. The router advertises this prefix to all nodes connected to that link, along with the length of the prefix, whether the prefix is on link (that is, a neighbor), whether the prefix can also be used for stateless address configuration, and the length of time the prefix is valid.
5. Manual Routes
   • Destination prefix
     The address prefix of a remote IPv6 network. The address prefix contains a Classless Inter-Domain Routing (CIDR) style bit length, for example, 5F00::/8. If you want to use the default route, write Default.
   • Interface
     The name of the interface through which you are sending traffic to the remote IPv6 network.
   • Next hop address
     The IPv6 address of the first router in the path to the destination prefix. Write the link local address of the router. If the connection to the router is over an IPv4 tunnel, write the link local IPv6 address of the remote tunnel endpoint.

When you run the TCPIP$IP6_SETUP configuration utility, it gathers information from the system and prompts you for additional configuration information.

2.2 IPv6 System Configuration Examples

This section shows how to use the configuration worksheet to assemble information for selected configurations. Each example shows how individual systems are configured. In some cases, additional options for you to consider are provided.

In a simple host-to-host configuration (shown in Figure 1-10), host A and host B use IPv6 link-local addresses. By default, the TCPIP$IP6_SETUP command configures the hosts automatically with a link-local address for your system. Figure 2-2 shows the completed worksheet for host A.

Figure 2-2 Simple Host-to-Host Configuration

After you configure IPv6 on host A, add a link-local address for host B to the TCPIP$ETC:IPNODES.DAT file. (For more information about these files, see Section 3.4.) The configuration process for host B in this configuration is similar to that for host A.

In this configuration, no global address prefix is advertised on the LAN. If you want to advertise a global address prefix, you can either configure one of the hosts as a router by using TCPIP$IP6_SETUP or add an IPv6 router to the LAN configuration. An IPv6 router advertises a global prefix on the link.

You can use the netstat -in command to view a local node's link-local and global addresses.

The following TELNET command connects host A to host B using host B's link-local address:

$ TELNET fe80::0a00:2bff:fee2:1e11

Alternately, you can place the address and node name in the TCPIP$ETC:IPNODES.DAT file. Then use the node name as the argument to the TELNET command. (For more information about this file, see Section 3.4.)

2.2.2 Host-to-Host with Router Configuration

In a host-to-host with router configuration (shown in Figure 1-11), host A and host B are on a LAN with router A. In this case, router A advertises the global address prefix dec:1:1::/64 on the LAN. Host A and host B use this address prefix to create global IPv6 addresses. (See Chapter 1 for information about obtaining experimental testing addresses.) Figure 2-3 shows the completed worksheet for router A.

Figure 2-3 Host-to-Host with Router Configuration

After you configure IPv6 on router A, add the global addresses for the other hosts to the TCPIP$ETC:IPNODES.DAT file. (For more information about this file, see Section 3.4.) Repeat this step on host A and host B. Alternatively, you could establish DNS/BIND in your network using the global addresses.