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- IPv6 Basics Overview, on page 1
- IPv6 Addressing, on page 1
- IPv6 Unicast Addresses: Network and Host IDs, on page 2
- Types of IPv6 Addresses, on page 3
- Address Assignment for IPv6 Devices, on page 6
- DNS for IPv6, on page 9
IPv6 Basics Overview
This chapter provides an introduction to the basics of IPv6 addressing, including the various address types, address assignment options, new DHCP features, and DNS. For further reading on IPv6, you can refer to the following documentation:
- IPv6 Fundamentals: A Straightforward Approach to Understanding IPv6, 2nd Edition , a Cisco Press publication available as a: book or video.
- IPv6 Design and Deployment LiveLessons , a Cisco Press publication available through http://www.ciscopress.com/store/ipv6-design-and-deployment-livelessons-
- Other Cisco online documentation at http://www.cisco.com/go/ipv
IPv6 Addressing
An IPv6 address consists of 8 sets of 16-bit hexadecimal values separated by colons (:), totaling 128 bits in length. For example:
2001:0db8:1234:5678:9abc:def0:1234:
You can omit leading zeros. For consecutive zeros in contiguous blocks, you can use a double colon (::). Double colons can appear only once in the address. For example, here is the complete address:
2001:0db8:0000:130F:0000:0000:087C:140B
IPv6 Basics
Here is the abbreviation:
2001:0db8:0:130F::87C:140B
As with IPv4 addresses, you can represent an IPv6 address network prefix the same way:
2001:db8:12::/
IPv6 Unicast Addresses: Network and Host IDs
IPv6 unicast addresses generally use 64 bits for the network ID and 64 bits for the host ID. Figure 1: Format for IPv6 Unicast Network ID and Host ID
The network ID is administratively assigned. The host ID is configured manually or auto-configured by any of the following methods:
- Using a randomly generated number.
- Using DHCPv6.
- Using the Extended Unique Identifier (EUI-64) format. We commonly use the EUI-64 host ID format for devices such as Cisco IP Phones, gateways, and routers. This format, as illustrated, expands the device interface 48-bit MAC address to 64 bits by inserting FFFE into the middle 16 bits.
Figure 2: Conversion of EUI-64 MAC Address to IPv6 Host Address Format
IPv6 Basics
IPv6 Unicast Addresses: Network and Host IDs
Figure 3: Format for Global Unicast Addresses
The global routing prefix is assigned to a service provider by the Internet Assigned Numbers Authority (IANA). The site level aggregator (SLA), or subnet ID, is assigned to a customer by their service provider. The LAN ID represents individual networks within the customer site and is administered by the customer. The Host or Interface ID has the same meaning for all unicast addresses. It is 64 bits long and is typically created by using the EUI-64 format. Example:
2001:0DB8:BBBB:CCCC:0987:65FF:FE01:
Unique Local Unicast Addresses
Unique local unicast addresses are:
- Analogous to private IPv4 addresses (for example, 10.1.1.254)
- Used for local communications, inter-site VPNs, and so forth
- Not routable on the Internet (routing would require IPv6 NAT)
Figure 4: Format of Local Unique Address
Global IDs do not have to be aggregated and are defined by the administrator of the local domain. Subnet IDs are also defined by the administrator of the local domain. Subnet IDs are typically defined using a hierarchical addressing plan to allow for route summarization. The Host or Interface ID has the same meaning for all unicast addresses. It is 64 bits long and is typically created by using the EUI-64 format.
IPv6 Basics
Unique Local Unicast Addresses
Example:
FD00:aaaa:bbbb:CCCC:0987:65FF:FE01:
Link Local Unicast Addresses
Link local unicast addresses are:
- Mandatory addresses that are used exclusively for communication between two IPv6 devices on the same link.
- Automatically assigned by device when IPv6 is enabled.
- Not routable addresses. Their scope is link-specific only.
- Identified by the first 10 bits (FE80).
Figure 5: Format of Link Local Unicast Address
The remaining 54 bits of the network ID could be zero or any manually configured value. The interface ID has the same meaning for all unicast addresses. It is 64 bits long and is typically created by using the EUI- format. Example:
FE80:0000:0000:0000:0987:65FF:FE01:
This address would generally be represented in shorthand notation as:
FE80::987:65FF:FE01:
IPv6 Multicast Addresses
IPv6 multicast addresses have an 8-bit prefix, FF00::/8 (1111 1111). The second octet defines the lifetime and scope of the multicast address. Figure 6: Multicast Address Format
Multicast addresses are always destination addresses. Multicast addresses are used for router solicitations (RS), router advertisements (RA), DHCPv6, multicast applications, and so forth.
IPv6 Basics
Link Local Unicast Addresses
IPv6 Stateless Address Auto-Configuration (RFC2462)
One of the easiest ways to assign IP addresses is to set up IPv6 Stateless address auto-configuration (SLAAC) on an IPv6 router. The network administrator configures the router to send Router Advertisement (RA) announcements onto the link. Then the on-link connected IPv6 nodes configure themselves with an IPv6 address and routing parameters. They get the IPv6 network prefix from the link-local router's RAs. They create the IPv6 host ID by using the device's MAC address and the EUI-64 format for host IDs.
DHCP for IPv
IPv6 devices use multicast to acquire IP addresses and to find DHCPv6 servers. The basic DHCPv6 client-server concept is similar to DHCP for IPv4. If a client wants to receive configuration parameters, it sends out a request on the attached local network to detect available DHCPv6 servers.
- The DHCPv6 client requests parameters from an available server. This is done using Solicit and Advertise message and well-known DHCPv6 multicast addresses.
- The server responds with the requested information in a Reply message. As with DHCPv4, DHCPv uses an architectural concept of "options" to carry more parameters and information within DHCPv messages.
Figure 7: IPv6 DHCP Messages
The DHCPv6 client knows whether to use DHCPv6 based upon the instruction from a router on its link-local network. The default gateway has two configurable bits in its Router Advertisement (RA) available for this purpose:
- O bitāWhen this bit is set, the client can use DHCPv6 to retrieve other configuration parameters (for example, TFTP server address or DNS server address) but not the client's IP address.
- M bitāWhen this bit is set, the client can use DHCPv6 to retrieve a managed IPv6 address and other configuration parameters from a DHCPv6 server.
IPv6 Basics
IPv6 Stateless Address Auto-Configuration (RFC2462)
Stateless DHCP
Stateless DHCPv6, which is specified by RFC3736, is a combination of Stateless address auto-configuration (SLAAC) and Dynamic Host Configuration Protocol (DHCP) for IPv6. When a router sends an RA with the O bit set but does not set the M bit, the client can use SLAAC to obtain its IPv6 address and use DHCPv6 to obtain additional information, such as TFTP server address or DNS server address. This mechanism is known as Stateless DHCPv6 because the DHCPv6 server does not have to track the client address bindings.
Stateful DHCP
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) has been standardized by the Internet Engineering Task Force (IETF) through RFC3315. When a router sends an RA with the M bit set, this indicates that clients should use DHCP to obtain their IP addresses. When the M bit is set, the setting of the O bit is irrelevant because the DHCP server also returns other configuration information together with the addresses. This mechanism is known as Stateful DHCPv6 because the DHCPv6 server tracks the client address bindings.
IPv6 Address Assignment Table
To automatically configure IP phones with IPv6 address assignment, use the following configuration in Unified CM and in router Routing Advertisement (RA).
Table 2: Automatic IPv6 Address Assignment
Auto_config parameter on M-bit O-bit Unified CM
Address Assignment Method
Stateful DHCPv6 for IP On On Off Phone address, TFTP and DNS address
IPv6 address Stateless On Off On prefix from RA and DHCP to pull TFTP and DNS address
Invalid configuration On Off Off
Stateful DHCPv6 for IP Off On Off Phone address, TFTP and DNS address
Invalid configuration Off Off On
Invalid configuration Off Off Off
IPv6 Basics
Stateless DHCP
IPv6 Basics
DNS for IPv
