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Appendix E IPv6
eircom F1000 Modem User’s Guide
341
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 four bits for each
character (1 ~ 10, A ~ F). Each block’s 16 bits are then represented by four 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.
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
FF08:0:0:0:0:0:0:0
FF09:0:0:0:0:0:0:0
FF0A:0:0:0:0:0:0:0
FF0B:0:0:0:0:0:0:0
FF0C:0:0:0:0:0:0:0
FF0D:0:0:0:0:0:0:0
FF0E:0:0:0:0:0:0:0
FF0F:0:0:0:0:0:0:0
Table 145
Reserved Multicast Address (continued)
MULTICAST ADDRESS
MAC
00
: 13
: 49
: 12
: 34
: 56
EUI-64
0
2
: 13
: 49
:
FF
:
FE
: 12
: 34
: 56
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Appendix E IPv6
eircom F1000 Modem User’s Guide
342
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.
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. An IPv6 device uses the following ICMPv6 messages types:
•
Neighbor solicitation: A request from a host to determine a neighbor’s link-layer address (MAC
address) and detect if the neighbor is still reachable. A neighbor being “reachable” means it
responds to a neighbor solicitation message (from the host) with a neighbor advertisement
message.
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
Page 343 / 359
Appendix E IPv6
eircom F1000 Modem User’s Guide
343
•
Neighbor advertisement: A response from a node to announce its link-layer address.
•
Router solicitation: A request from a host to locate a router that can act as the default router and
forward packets.
•
Router advertisement: A response to a router solicitation or a periodical multicast advertisement
from a router to advertise its presence and other parameters.
IPv6 Cache
An IPv6 host is required to have a neighbor cache, destination cache, prefix list and default router
list. The Device maintains and updates its IPv6 caches constantly using the information from
response messages. In IPv6, the Device configures a link-local address automatically, and then
sends a neighbor solicitation message to check if the address is unique. If there is an address to be
resolved or verified, the Device also sends out a neighbor solicitation message. When the Device
receives a neighbor advertisement in response, it stores the neighbor’s link-layer address in the
neighbor cache. When the Device uses a router solicitation message to query for a router and
receives a router advertisement message, it adds the router’s information to the neighbor cache,
prefix list and destination cache. The Device creates an entry in the default router list cache if the
router can be used as a default router.
When the Device needs to send a packet, it first consults the destination cache to determine the
next hop. If there is no matching entry in the destination cache, the Device uses the prefix list to
determine whether the destination address is on-link and can be reached directly without passing
through a router. If the address is unlink, the address is considered as the next hop. Otherwise, the
Device determines the next-hop from the default router list or routing table. Once the next hop IP
address is known, the Device looks into the neighbor cache to get the link-layer address and sends
the packet when the neighbor is reachable. If the Device cannot find an entry in the neighbor cache
or the state for the neighbor is not reachable, it starts the address resolution process. This helps
reduce the number of IPv6 solicitation and advertisement messages.
Multicast Listener Discovery
The Multicast Listener Discovery (MLD) protocol (defined in RFC 2710) is derived from IPv4's
Internet Group Management Protocol version 2 (IGMPv2). MLD uses ICMPv6 message types, rather
than IGMP message types. MLDv1 is equivalent to IGMPv2 and MLDv2 is equivalent to IGMPv3.
MLD allows an IPv6 switch or router to discover the presence of MLD listeners who wish to receive
multicast packets and the IP addresses of multicast groups the hosts want to join on its network.
MLD snooping and MLD proxy are analogous to IGMP snooping and IGMP proxy in IPv4.
MLD filtering controls which multicast groups a port can join.
MLD Messages
A multicast router or switch periodically sends general queries to MLD hosts to update the multicast
forwarding table. When an MLD host wants to join a multicast group, it sends an MLD Report
message for that address.
An MLD Done message is equivalent to an IGMP Leave message. When an MLD host wants to leave
a multicast group, it can send a Done message to the router or switch. The router or switch then
sends a group-specific query to the port on which the Done message is received to determine if
other devices connected to this port should remain in the group.
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Appendix E IPv6
eircom F1000 Modem User’s Guide
344
Example - Enabling IPv6 on Windows XP/2003/Vista
By default, Windows XP and Windows 2003 support IPv6. This example shows you how to use the
ipv6 install
command on Windows XP/2003 to enable IPv6. This also displays how to use the
ipconfig
command to see auto-generated IP addresses.
IPv6 is installed and enabled by default in Windows Vista. Use the
ipconfig
command to check
your automatic configured IPv6 address as well. You should see at least one IPv6 address available
for the interface on your computer.
Example - Enabling DHCPv6 on Windows XP
Windows XP does not support DHCPv6. If your network uses DHCPv6 for IP address assignment,
you have to additionally install a DHCPv6 client software on your Windows XP. (Note: If you use
static IP addresses or Router Advertisement for IPv6 address assignment in your network, ignore
this section.)
This example uses Dibbler as the DHCPv6 client. To enable DHCPv6 client on your computer:
1
Install Dibbler and select the DHCPv6 client option on your computer.
2
After the installation is complete, select
Start
>
All Programs
>
Dibbler-DHCPv6
>
Client
Install as service
.
3
Select
Start
>
Control Panel
>
Administrative Tools
>
Services
.
C:\>ipv6 install
Installing...
Succeeded.
C:\>ipconfig
Windows IP Configuration
Ethernet adapter Local Area Connection:
Connection-specific DNS Suffix
. :
IP Address. . . . . . . . . . . . : 10.1.1.46
Subnet Mask . . . . . . . . . . . : 255.255.255.0
IP Address. . . . . . . . . . . . : fe80::2d0:59ff:feb8:103c%4
Default Gateway . . . . . . . . . : 10.1.1.254
Page 345 / 359
Appendix E IPv6
eircom F1000 Modem User’s Guide
345
4
Double click
Dibbler - a DHCPv6 client
.
5
Click
Start
and then
OK
.
6
Now your computer can obtain an IPv6 address from a DHCPv6 server.
Example - Enabling IPv6 on Windows 7
Windows 7 supports IPv6 by default. DHCPv6 is also enabled when you enable IPv6 on a Windows 7
computer.
To enable IPv6 in Windows 7:
1
Select
Control Panel
>
Network and Sharing Center
>
Local Area Connection
.
2
Select the
Internet Protocol Version 6 (TCP/IPv6)
checkbox to enable it.
3
Click
OK
to save the change.

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