ZyXEL Communications P-2812HNU-51c User Manual page 367

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, such as the system name. The interface-ID
option provides slot number, port information and the VLAN ID to the DHCPv6
server. The remote-ID option (if any) is stripped from the Relay-Reply messages
before the relay agent sends the packets to the clients. The DHCP server copies
the interface-ID option from the Relay-Forward message into the Relay-Reply
message and sends it to the relay agent. The interface-ID should not change even
after the relay agent restarts.
Prefix Delegation
Prefix delegation enables an IPv6 router to use the IPv6 prefix (network address)
received from the ISP (or a connected uplink router) for its LAN. The Device uses
the received IPv6 prefix (for example, 2001:db2::/48) to generate its LAN IP
address. Through sending Router Advertisements (RAs) regularly by multicast, the
Device passes the IPv6 prefix information to its LAN hosts. The hosts then can use
the prefix to generate their IPv6 addresses.
P-2612HNU-Fx User's Guide
T1
Renew
to S1
Renew
to S1
T2
Renew
Renew
to S1
to S1
Renew
Renew
to S1
to S1
Appendix F IPv6
Rebind
to S2
Rebind
to S2
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