Dynamic Host Configuration Protocol version 6 (DHCPv6) is an updated version of DHCP that provides dynamic IP address assignment for IPv6 hosts. DHCPv6, described in RFC 3315, provides the same functions as DHCP, with more control than stateless autoconfiguration, and it supports renumbering without routers. DHCPv6 assignment is stateful, whereas IPv6 link-local and globally unique autoconfiguration are not.
DHCPv6 Lite
SLAAC is simpler than DHCPv6, although it offers less control and fewer capabilities. For example, SLAAC is not able to send DNS parameters. To overcome this limitation, there is another (special case) option for clients to receive both their IPv6 address and other information statelessly. This is accomplished using SLAAC initially and then using stateless DHCPv6 service, also known as DHCPv6 Lite. With DHCPv6 Lite, DNS server, domain name, SIP server, and other information can be sent to the client. With DHCPv6 Lite, the client performs the SLAAC to obtain its IPv6 address and then sends a DHCP information request to the router. The router then responds with a reply message in the requested information.
IPv6 Security
IPv6 has two integrated mechanisms to provide security for communications. It natively supports IP Security (IPsec), which is mandated at the operating system level for all IPsec hosts. RFC 2401 describes IPsec. Extension headers carry the IPsec AH and ESP headers. The AH provides authentication and integrity. The ESP header provides confidentiality by encrypting the payload. For IPv6, the AH defaults to Message Digest Algorithm 5 (MD5), and the ESP encryption defaults to Data Encryption Standard–Cipher Block Chaining (DES-CBC).
A description of the IPsec mechanisms appears in Chapter 8, “WAN for Enterprise.” More information also appears in RFC 2402: IP Authentication Header and in RFC 2406: IP Encapsulating Security Payload (ESP).
Table 2-9 summarizes IPv6 mechanisms.
Table 2-9 IPv6 Mechanisms
| IPv6 Mechanism | Description |
| ICMPv6 | Performs diagnostics and reachability information. Has a Next Header number of 58. |
| IPv6 Neighbor Discovery | Discovers all nodes in the same link and checks for duplicate addresses. |
| AAAA | Indicates the DNS resource record for IPv6. |
| SLAAC | Performs stateless IPv6 address assignment. |
| DHCPv6 | Provides stateful IPv6 address assignment. |
| RIPng | Routing protocol that uses UDP port 521. |
| EIGRP for IPv6 | Cisco routing protocol for IPv6. |
| OSPFv3 | Link-state routing protocol for IPv6. |
IPv6 Routing Protocols
New routing protocols have been developed to support IPv6, such as RIPng, Intermediate System-to-Intermediate System (IS-IS), Enhanced Interior Gateway Routing Protocol (EIGRP) for IPv6, and Open Shortest Path First Version 3 (OSPFv3). Border Gateway Protocol (BGP) also includes changes that support IPv6. These routing protocols are only briefly mentioned here because they are covered in detail in Chapter 3, “Routing Protocol Characteristics, EIGRP, and IS-IS,” and Chapter 4, “OSPF, BGP, and Route Manipulation.”