SOLICIT (1)

  A DHCPv6 client sends a Solicit message to locate DHCPv6 servers.

ADVERTISE (2)

A server sends an Advertise message to indicate that it is available for DHCP service, in response to a Solicit message received from a client.

REQUEST (3)

A client sends a Request message to request configuration parameters, including IP addresses or delegated prefixes, from a specific server.

CONFIRM (4)

A client sends a Confirm message to any available server to determine whether the addresses it was assigned are still appropriate to the link to which the client is connected. This could happen when the client detects either a link-layer connectivity change or if it is powered on and one or more leases are still valid. The confirm message is used to confirm whether the client is still on the same link or whether it has been moved. The actual lease(s) are not validated; just the prefix portion of the addresses or delegated prefixes.

RENEW (5)

A client sends a Renew message to the server that originally provided the client's addresses and configuration parameters to extend the lifetimes on the addresses assigned to the client and to update other configuration parameters.

REBIND (6)

A client sends a Rebind message to any available server to extend the lifetimes on the addresses assigned to the client and to update other configuration parameters; this message is sent after a client receives no response to a Renew message.

REPLY (7)

A server sends a Reply message containing assigned addresses and configuration parameters in response to a Solicit, Request, Renew, Rebind message received from a client. A server sends a Reply message containing configuration parameters in response to an Information-request message. A server sends a Reply message in response to a Confirm message confirming or denying that the addresses assigned to the client are appropriate to the link to which the client is connected. A server sends a Reply message to acknowledge receipt of a Release or Decline message.

RELEASE (8)

A client sends a Release message to the server that assigned addresses to the client to indicate that the client will no longer use one or more of the assigned addresses.

DECLINE (9)

A client sends a Decline message to a server to indicate that the client has determined that one or more addresses assigned by the server are already in use on the link to which the client is connected.

RECONFIGURE (10)

A server sends a Reconfigure message to a client to inform the client that the server has new or updated configuration parameters, and that the client is to initiate a Renew/Reply or Information-request/Reply transaction with the server in order to receive the updated information.

INFORMATION-REQUEST (11)

A client sends an Information-request message to a server to request configuration parameters without the assignment of any IP addresses to the client.

RELAY-FORW (12)

A relay agent sends a Relay-forward message to relay messages to servers, either directly or through another relay agent. The received message, either a client message or a Relay-forward message from another relay agent, is encapsulated in an option in the Relay-forward message.

RELAY-REPL (13)

A server sends a Relay-reply message to a relay agent containing a message that the relay agent delivers to a client. The Relay-reply message may be relayed by other relay agents for delivery to the destination relay agent. The server encapsulates the client message as an option in the Relay-reply message, which the relay agent extracts and relays to the client.

DHCPv6 Options Within DHCPv6, options are used to exchange parameter information between a server and a client. If a client wishes to request a specific option or set of parameters it must do this through an ORO option (Option Request Option). Cisco IOS only supports a limited set of options from the full list of options available at IANA ( http://www.iana.org/assignments/dhcpv6-parameters). Options have a 16 bit option number and 16 bit option lengths. Some options will encapsulate other options for scoping purposes. A DHCPv6 relay will encapsulate client (or other relay) messages in a message option. The following options are amongst others supported by Cisco IOS:

• Client Identifier option

– The Client Identifier option is used to carry a DUID identifying a client between a client and a server

• · Server Identifier option

– The Server Identifier option is used to carry a DUID identifying a server between a client and a server

• Option Request option

– The Option Request option is used to identify a list of options in a message between a client and a server.

• Preference option

– The Preference option is sent by a server to a client to affect the selection of a server by the client

• Status Code Option

– This option returns a status indication related to the DHCP message or option in which it appears

• Rapid Commit option

– The Rapid Commit option is used to signal the use of the two message exchange for address assignment

• Identity Association for Prefix Delegation option (IA_PD option)

– The IA_PD option is used to carry a prefix delegation identity association, the parameters associated with the IA_PD and the prefixes associated with it

• IA_PD Prefix option

– The IA_PD Prefix option is used to specify IPv6 address prefixes associated with an IA_PD. The IA_PD Prefix option must be encapsulated in the IA_PD-options field of an IA_PD option.

• Domain Name Server option

– The DNS Recursive Name Server option provides a list of one or more IPv6 addresses of DNS recursive name servers to which a client's DNS resolver MAY send DNS queries. The DNS servers are listed in the order of preference for use by the client resolver.

• Domain Search List option

– The Domain Search List option specifies the domain search list the client is to use when resolving hostnames with DNS. This option does not apply to other name resolution mechanisms.

• Information Refresh Option

– The Information Refresh Option is used for specifying an upper bound for how long a client should wait before refreshing information retrieved from DHCPv6. It is used with stateless DHCPv6 as there are no addresses or other entities with lifetimes that can tell the client when to contact the DHCPv6 server to refresh its configuration.

• Remote-id option

– This option may be added by DHCPv6 relay agents that terminate switched or permanent circuits and have mechanisms to identify the remote host end of the circuit.