Zyxel VMG3926-B10A Router Manual PDF (Setup & Configuration Guide)

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VMG3926-B10A User’s Guide

301

PPENDIX

IPv6

Overview

IPv6 (Internet Protocol version 6), is designed to enhance IP address size and features. The

increase in IPv6 address size to 128 bits (from the 32-bit IPv4 address) allows up to 3.4 x 10

addresses.

IPv6 Addressing

The 128-bit IPv6 address is written as eight 16-bit hexadecimal blocks separated by colons (:). This

is an example IPv6 address

2001:0db8:1a2b:0015:0000:0000:1a2f:0000

IPv6 addresses can be abbreviated in two ways:

•

Leading zeros in a block can be omitted. So

2001:0db8:1a2b:0015:0000:0000:1a2f:0000

can

be written as

2001:db8:1a2b:15:0:0:1a2f:0

•

Any number of consecutive blocks of zeros can be replaced by a double colon. A double colon can

only appear once in an IPv6 address. So

2001:0db8:0000:0000:1a2f:0000:0000:0015

can be

written as

2001:0db8::1a2f:0000:0000:0015

2001:0db8:0000:0000:1a2f::0015

2001:db8::1a2f:0:0:15

2001:db8:0:0:1a2f::15

Prefix and Prefix Length

Similar to an IPv4 subnet mask, IPv6 uses an address prefix to represent the network address. An

IPv6 prefix length specifies how many most significant bits (start from the left) in the address

compose the network address. The prefix length is written as “/x” where x is a number. For

example,

2001:db8:1a2b:15::1a2f:0/32

means that the first 32 bits (

2001:db8

) is the subnet prefix.

Link-local Address

A link-local address uniquely identifies a device on the local network (the LAN). It is similar to a

“private IP address” in IPv4. You can have the same link-local address on multiple interfaces on a

device. A link-local unicast address has a predefined prefix of fe80::/10. The link-local unicast

address format is as follows.

Table 130

Link-local Unicast Address Format

1111 1110 10

Interface ID

10 bits

54 bits

64 bits

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Global Address

A global address uniquely identifies a device on the Internet. It is similar to a “public IP address” in

IPv4. A global unicast address starts with a 2 or 3.

Unspecified Address

An unspecified address (0:0:0:0:0:0:0:0 or ::) is used as the source address when a device does

not have its own address. It is similar to “0.0.0.0” in IPv4.

Loopback Address

A loopback address (0:0:0:0:0:0:0:1 or ::1) allows a host to send packets to itself. It is similar to

“127.0.0.1” in IPv4.

Multicast Address

In IPv6, multicast addresses provide the same functionality as IPv4 broadcast addresses.

Broadcasting is not supported in IPv6. A multicast address allows a host to send packets to all hosts

in a multicast group.

Multicast scope allows you to determine the size of the multicast group. A multicast address has a

predefined prefix of ff00::/8. The following table describes some of the predefined multicast

addresses.

The following table describes the multicast addresses which are reserved and can not be assigned

to a multicast group.

Table 131

Predefined Multicast Address

MULTICAST ADDRESS

DESCRIPTION

FF01:0:0:0:0:0:0:1

All hosts on a local node.

FF01:0:0:0:0:0:0:2

All routers on a local node.

FF02:0:0:0:0:0:0:1

All hosts on a local connected link.

FF02:0:0:0:0:0:0:2

All routers on a local connected link.

FF05:0:0:0:0:0:0:2

All routers on a local site.

FF05:0:0:0:0:0:1:3

All DHCP severs on a local site.

Table 132

Reserved Multicast Address

MULTICAST ADDRESS

FF00:0:0:0:0:0:0:0

FF01:0:0:0:0:0:0:0

FF02:0:0:0:0:0:0:0

FF03:0:0:0:0:0:0:0

FF04:0:0:0:0:0:0:0

FF05:0:0:0:0:0:0:0

FF06:0:0:0:0:0:0:0

FF07:0:0:0:0:0:0:0

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Appendix C IPv6

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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 (

) (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 132

Reserved Multicast Address (continued)

MULTICAST ADDRESS

MAC

: 13

: 49

: 12

: 34

: 56

EUI-64

: 13

: 49

: 12

: 34

: 56

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Appendix C IPv6

VMG3926-B10A User’s Guide

304

the time T2 is reached and the server does not respond, the client sends a Rebind message to any

available server (

). 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 VMG 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 VMG 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.

Renew

Rebind

to S1

Renew

to S1

Renew

to S1

Renew

to S1

Renew

to S1

Renew

to S1

to S2

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Appendix C IPv6

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305

•

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 VMG maintains and updates its IPv6 caches constantly using the information from

response messages. In IPv6, the VMG 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 VMG also sends out a neighbor solicitation message. When the VMG

receives a neighbor advertisement in response, it stores the neighbor’s link-layer address in the

neighbor cache. When the VMG 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 VMG creates an entry in the default router list cache if the

router can be used as a default router.

When the VMG 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 VMG 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

VMG determines the next-hop from the default router list or routing table. Once the next hop IP

address is known, the VMG looks into the neighbor cache to get the link-layer address and sends

the packet when the neighbor is reachable. If the VMG 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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