ZyXEL Communications IES4005M User Manual page 147

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.
ICMPv6
Internet Control Message Protocol for IPv6 (ICMPv6 or ICMP for IPv6) is defined in RFC 4443.
ICMPv6 has a preceding Next Header value of 58, which is different from the value used to identify
ICMP for IPv4. ICMPv6 is an integral part of IPv6. IPv6 nodes use ICMPv6 to report errors
encountered in packet processing and perform other diagnostic functions, such as "ping".
Neighbor Discovery Protocol (NDP)
The Neighbor Discovery Protocol (NDP) is a protocol used to discover other IPv6 devices and track
neighbor's reachability in a network. A neighbor is "reachable" means a neighbor solicitation
message (from the IES) is responded with a neighbor advertisement message from the neighbor.
IES4005M User's Guide
T1
Renew
to S1
Renew
to S1
T2
Renew
Renew
to S1
to S1
Renew
Renew
to S1
to S1
Chapter 19 IPv6
Rebind
to S2
Rebind
to S2
147