Chapter 33 IPv6 Commands
Ethernet Switch CLI Reference Guide
143
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, 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 copys 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".
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
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