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Appendix C IPv6
XGS2220 Series User’s Guide
704
Subnet Masking
Both an IPv6 address and IPv6 subnet mask compose of 128-bit binary digits, which are divided into
eight 16-bit blocks and written in hexadecimal notation. Hexadecimal uses 4 bits for each character (1 –
10, A – F). Each block’s 16 bits are then represented by 4 hexadecimal characters. For example,
FFFF:FFFF:FFFF:FFFF:FC00:0000:0000:0000.
Interface ID
In IPv6, an interface ID is a 64-bit identifier. It identifies a physical interface (for example, an Ethernet
port) or a virtual interface (for example, the management IP address for a VLAN). One interface should
have a unique interface ID.
EUI-64
The EUI-64 (Extended Unique Identifier) defined by the IEEE (Institute of Electrical and Electronics
Engineers) is an interface ID format designed to adapt with IPv6. It is derived from the 48-bit (6-byte)
Ethernet MAC address as shown next. EUI-64 inserts the hex digits fffe between the third and fourth bytes
of the MAC address and complements the seventh bit of the first byte of the MAC address. See the
following example.
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
Table 371
MAC 00 : 13 : 49 : 12 : 34 : 56
Table 372
EUI-64 02 : 13 : 49 : FF : FE : 12 : 34 : 56
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