Section B.11. DHCPv6 and Multicast Addresses for SLP over IPv6 (Chapter 9)

B.11. DHCPv6 and Multicast Addresses for SLP over IPv6 (Chapter 9)

The DHCPv6 messages types shown in Table B-26 have been specified in RFC 3315.

Table B-26. DHCPv6 message types

Message type



Used by clients to locate DHCP servers.


Used by servers as a response to Solicit.


Used by clients to get information from servers.


Used by clients to verify that their address and configuration parameters are still valid for their link.


Used by clients to extend the lifetime of their IP address and renew their configuration parameters with their original DHCP server when their lease is about to expire.


Used by clients to extend the lifetime of their address(es) and renew their configuration parameters with any DHCP server when their lease is about to expire and they have not received a reply to their Renew message.


Used by DHCP servers to respond to Solicit messages with a Rapid Commit Option, as well as to Request, Renew, and Rebind messages. A Reply to an Information Request message contains only configuration parameters, but no IP address. A Reply to a Confirm message contains a confirmation that the client's IP address(es) are still valid for the link (or a decline). A server sends a Reply as an acknowledgment for a Release or Decline message.


Used by clients to release their IP address. The message is sent to the server, from which the address was received.


Used by clients to indicate to the server that one or more addresses assigned to them are already in use on the link. This is determined by the client through Duplicate Address Detection (DAD).


Used by DHCP servers to inform clients that the server has new or updated configuration information. The clients then must initiate a Renew or Information Request message in order to obtain the updated information.


Sent by clients to request additional configuration parameters (without IP address information).


Used by DHCP relays to forward client messages to servers. The relay encapsulates the client message in an option in the Relay Forward message. The message can be sent directly to a DHCP server or via other relay agents. If a DHCP message is relayed multiple times, it is encapsulated multiple times.


Used by DHCP servers to send messages to clients through a relay. The client message is encapsulated as an option in the Relay Reply message. The relay decapsulates the message and forwards it to the client. The Relay Reply message takes the same path back through which the Relay Forward message traveled and may therefore also be encapsulated multiple times if there is more than one relay agent on the path.

Table 2-27 shows an overview of possible DHCP options defined in RFC 3315.

Table 2-27. DHCP options




Client Identifier


Used for the client DUID. A DUID is a unique identifier (described later in this chapter).

Server Identifier


Used for the server DUID.

Identity Association for Nontemporary Addresses (IA_NA)


Used to indicate the IA_NA, the parameters, and the nontemporary addresses associated with it.

Identity Association for Temporary Adresses (IA_TA)


Used to indicate the IA_TA, the parameters, and the temporary addresses associated to it. All addresses contained in this option are used as temporary addresses by the client (according to RFC 3041 on Privacy Extensions for Stateless Address Autoconfiguration).

IA Address


Used to indicate the addresses associated with an IA_NA or IA_TA.

Option Request


Used in a message between client and server to identify a list of options. Can be contained in a Request, Renew, Rebind, Confirm, or Information Request message. The server can use this option in a Reconfigure message to indicate which options have been changed or added.



Sent by the server to influence the choice of a client for a DHCP server.

Elapsed Time


Contains the time when the client started the DHCP transaction. Indicated in hundredths of a second. In the first message sent by a client it is set to 0. Can be used by a secondary DHCP server to detect whether a primary server responds in time.

Relay Message


Contains the original message in a Relay Forward or Relay Reply message (remember that the original message is encapsulated in a Relay Forward or Reply message).



Contains information to authenticate the identity and the content of DHCP messages.

Server Unicast


The server sends this option to the client to indicate that unicast can be used for communication. The option contains the IP address of the DHCP server, which is to be used by the client.

Table B-28 lists the multicast addresses that have been defined for SLP over IPv6.

Table B-28. Multicast addresses for SLP over IPv6

Multicast address



Service Agent (SA), used for Service Type and Attribute Request Messages.


Directory Agent (DA), used by User Agents (UAs) and SAs to discover DAs. Also used by DA for sending unsolicited DA Advertisement messages.

FF0X:0:0:0:0:0:1:1000 to FF0X:0:0:0:0:0:1:13FF

Service Location, used by SAs to join the groups that correspond to the Service Types of the services they advertise. The Service Type string is used to determine the corresponding value in the 1000 to 13FF range, which has been assigned by IANA for this purpose. For an explanation of the algorithm used to calculate the group ID, refer to RFC 3111.

The X in FF0X is the placeholder for the multicast scope to be used for this group ID. For instance, 2 is link-local scope and 5 is site-local scope.

IPv6 Essentials
IPv6 Essentials
ISBN: 0596100582
EAN: 2147483647
Year: 2004
Pages: 156
Authors: Silvia Hagen

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