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Appendix E IPv6
FMG3024-D10A / FMG3025-D10A Series User’s Guide
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combines its interface ID and global and subnet information advertised from the router. This is a
routable global IP address.
DHCPv6
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6, RFC 3315) is a server-client protocol
that allows a DHCP server to assign and pass IPv6 network addresses, prefixes and other
configuration information to DHCP clients. DHCPv6 servers and clients exchange DHCP messages
using UDP.
Each DHCP client and server has a unique DHCP Unique IDentifier (DUID), which is used for
identification when they are exchanging DHCPv6 messages. The DUID is generated from the MAC
address, time, vendor assigned ID and/or the vendor's private enterprise number registered with
the IANA. It should not change over time even after you reboot the device.
Identity Association
An Identity Association (IA) is a collection of addresses assigned to a DHCP client, through which
the server and client can manage a set of related IP addresses. Each IA must be associated with
exactly one interface. The DHCP client uses the IA assigned to an interface to obtain configuration
from a DHCP server for that interface. Each IA consists of a unique IAID and associated IP
information.
The IA type is the type of address in the IA. Each IA holds one type of address. IA_NA means an
identity association for non-temporary addresses and IA_TA is an identity association for temporary
addresses. An IA_NA option contains the T1 and T2 fields, but an IA_TA option does not. The
DHCPv6 server uses T1 and T2 to control the time at which the client contacts with the server to
extend the lifetimes on any addresses in the IA_NA before the lifetimes expire. After T1, the client
sends the server (S1) (from which the addresses in the IA_NA were obtained) a Renew message. If
the time T2 is reached and the server does not respond, the client sends a Rebind message to any
available server (S2). For an IA_TA, the client may send a Renew or Rebind message at the client's
discretion.
DHCP Relay Agent
A DHCP relay agent is on the same network as the DHCP clients and helps forward messages
between the DHCP server and clients. When a client cannot use its link-local address and a well-
known multicast address to locate a DHCP server on its network, it then needs a DHCP relay agent
to send a message to a DHCP server that is not attached to the same network.
The DHCP relay agent can add the remote identification (remote-ID) option and the interface-ID
option to the Relay-Forward DHCPv6 messages. The remote-ID option carries a user-defined string,
3. In IPv6, all network interfaces can be associated with several addresses.
T1
T2
Renew
Rebind
Rebind
to S1
Renew
to S1
Renew
to S1
Renew
to S1
Renew
to S1
Renew
to S1
to S2
to S2