attachment_learning service express(11)--ipv6 technology overview

8/11/2019 Attachment_Learning Service Express(11)--IPv6 Technology Overview

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IPv6 Technology Overview

IPv6 Features

Internet Protocol Version 6 (IPv6) is also called IP Next Generation (IPng). It is a

new version of the Internet Protocol, designed as the successor to IPv4. The

specifications and standardizations provided by it are consistent with the Internet

Engineering Task Force (IETF).

The difference between IPv6 and IPv4 is that an IPv4 address has 32 bits while an

IPv6 address has 128 bits.

The following sections describe the features of IPv6.

New Header Format

The IPv6 header has a new format that minimizes the header overload. The

nonessential fields and the option fields are carried in the extension headers that

are placed after the IPv6 header. The streamlined IPv6 header facilitates the router

to process the packets. The new IPv6 header is only twice as long as the IPv4header, even though the IPv6 address is four times as long as the IPv4 address.

The IPv6 protocol is not compatible with the IPv4 protocol. A host or router mustrun IPv4 and IPv6 to recognize and process the two header formats.


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Figure 8-1Comparison between IPv4 and IPv6 packet headers

Large Address Space

The IPv6 source and destination addresses are both 16 bytes, which can provide

over 3.41038

possible combinations. In this way, the need for multiple levels of

public and private address is met. Since IPv6 provides abundant IP addresses,

address conservation, such as NAT, is not needed.

Hierarchical Address Structure

The IPv6 address has a hierarchical structure to facilitate searching routes. In

addition, the system resources occupied by the IPv6 routing table are reduced

efficiently with the router aggregation.

Stateless and Stateful Addresses Automatic Configuration

To simplify the host configuration, IPv6 supports auto configuring stateful and

stateless addresses. In the stateless address automatic configuration, hosts on a

link automatically configure an IPv6 addresses for the local link with the prefixadvertised by the router. If the router does not exist, the local link address can still

be automatically configured.

31

Total length

Identification

0

TTLSource address (32 bits)

Padding

TOSIHL

Fragment offsetF

Protocol Header checksum

Destination address (32 bits)

Options

157

IPv4 header

31

Version Flow label

Prototype length

0

Source address (128 bits)

Traffic class

Hop limitNext header

157

Destination address(128 bits)

IPv6 header

Version


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Built-in Security

IPv6 takes IPSec as its standard extension header, which provides an end-to-end

security protection. This build-in security also promotes interoperability betweendifferent IPv6 services.

Supporting QoS

A new filed, Flow Label, in the IPv6 header allows a router to identify packets in

a flow. A flow is a group of packets from a source address to a destination address.Since IPv6 header can identify flows, IPv6 can guarantee QoS to the packet

payloads even with IPSec encryption.

Flow, a group pf packets sent from the source to the destination, should match certaintraffic classifications.

Enhanced Neighbor Discovery Mechanism

The Neighbor Discovery (ND) protocol for IPv6 is a series of Internet Control

Message Protocol for IPv6 (ICMP6) messages. The ICMP6 manages theinteraction of neighboring nodes (that is, nodes on the same link). The ND

replaces the Address Resolution Protocol (ARP), ICMPv4 router Discovery, and

ICMPv4 Redirect messages with efficient multicast and unicast messages andprovides additional functionalities.

Flexible Header Extensibility

The IPv6 does not use the option field in the IPv4 header and introduces multiple

extension headers in the IPv6 header. This improves the efficiency of IPv6 andprovides fine extensibility for IP protocols. Unlike the IPv4 header, which can

only support 40 bytes of options, the size of IPv6 extension headers is constrainedonly a by the size of the IPv6 packet.

IPv6 Addresses

Format of an IPv6 Address

An IPv6 address typically has two major 64-bit parts: the network prefixoccupies

the higher order groups of bits and the interface IDoccupies the lower ones. An

IPv6 address prefix is represented as IPv6-address/prefix-length, similar to theIPv4 address prefixes written in the IPv4 Classless Inter-domain Routing (CIDR).

x:x:x:x:x:x:x:xIPv6 introduces a new 128-bit addressing model. In this format, the 128 bits in the

IPv6 address space are broken down into eight groups of 16 bits, each of whichcan be represented with four hexadecimal values (0 to 9, and A to F). The groups

are separated by colons. The text address then reads x:x:x:x:x:x:x:x, in which eachx represents a given hexadecimal value.

An example of typical addresses is 2031:0000:130F:0000:0000:09C0:876A:130B.For convenience, the preceding 0s in each group can be omitted, and hence the

NOTE


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address given above is written as 2031:0:130F:0:0:9C0:876A:130B. In addition, it

is acceptable to substitute a pair of colons "::" anywhere in the address to

represent two or more 16-bit groups of zeros in a string and thus compress thelength of the address. The address given above would then be written as

2031:0:130F::9C0:876A:130B.

An address may not contain more than one set of paired colons as a computer expands the"::" with 0 to get 128 bits; hence it cannot decide on the number of zeros in each segment.

x:x:x:x:x:x:d.d.d.d

An alternative format for the address is x:x:x:x:x:x:d.d.d.d, in which x represents

hexadecimal values of the six higher-order 16-bit pieces and d represents decimalvalues of the four lower-order 8-bit pieces. The latter portion is the standard IPv4

address.

This format is not recommended. It is commonly used during the configuration of

IPv6-over-IPv4 tunnels.

IPv6 Address Classification

There are three major types of addresses: unicast, anycast,andmulticast.

Unicast address: identifies a single interface. It is equivalent to an IPv4

unicast address. The packets sent to a unicast address are transmitted to asingle interface identified by this address.

Anycast address: identifies a group of interfaces, which usually belong to

different nodes. The packets sent to an anycast address are transmitted to one

of the identified interfaces which are near to the source node (the distance ismeasured by the routing protocol).

Multicast address: comprises a set of interfaces, which usually belong to

different nodes. It is similar to IPv4 multicast addresses. The packets sent toa multicast address are transmitted to all the interfaces identified by thisaddress.

IPv6 does not include broadcast addresses. It is the multicast addresses that

provide the broadcast function.

Unicast Address Types

A unicast address controls one-to-one transmission. Similar to the unicast IPv4

address, it identifies a single interface and delivers packets to this address.

The unicast IPv6 addresses are summarized as follows.

Table 8-1Summary of unicast IPv6 addresses

Address Type Binary Prefix IPv6 Notation

Link-local unicast address 1111111010 FE80::/10

Site-local unicast address 1111111011 FEC0::/10

Loopback address 00...1 (128 bits) ::1/128

NOTE


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Address Type Binary Prefix IPv6 Notation

Unspecified address 00...0(128 bits) ::/128

Global unicast address others -

The global unicast address is equivalent to the IPv4 public network address.It is used on links that are aggregated upwards through an organization and is

eventually provided to the ISP. The structure of this type of address enables

policies that allow aggregation of routing prefixes to limit the number ofentries in the global routing table. The address consists of a 48-bit routing

prefix managed by the provider, a 16-bit subnet ID managed by the local site,and a 64-bit interface ID.

A link-local unicast address is used to communicate among nodes on a locallink, in the neighbor discovery protocol, and in the stateless auto

configuration process. The packets with a link-local unicast address as its

source address or destination address are not transmitted to other links. It can

be automatically configured on any interface by using the link-local prefixFE80::/10(1111 1110 10) and the interface identifier in the IEEE EUI-64format (a EUI-64 may be derived from an EUI-48).

A site-local unicast address is similar to an IPv4 private address, for example,

172.16.0.0/12. The prefix does not spread between routing domains and thisrestricts communication with a specific domain. The packets with a site-local

unicast address as its source address or destination address are nottransmitted to other sites.

The unicast address 0:0:0:0:0:0:0:1 or ::1 is a loopback address. It cannot beassigned to any interface. It performs the same function as the 127.0.0.1 inthe IPv4 - identifying a transmission sent by a node, back to itself.

Unspecified address.

Interface ID of the IEEE EUI-64 Format

The 64-bit interface ID in the IPv6 address identifies a single interface on the link.

This address derives from the link layer address (MAC address for example) of

the interface. The interface ID of the IPv6 address has 64 bits, while MAC address

has 48 bits. Therefore, insert a hexadecimal number FFFE (11111111 11111110) in

the middle of the MAC address. To ensure that the interface ID is unique, set theU/L bit (the seventh bit from the higher part) to 1. This group of numbers serves

as the interface ID of the EUI-64 format.


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Figure 8-2Translation process from MAC address to the EUI-64 address

0000000 00010010 00110100 00000000 10101011 11001101

00000000 00010010 00110100 1111111111111110 00000000 1010101111001101

0012:3400:ABCD

00000010 00010010 00110100 11111111 11111110 00000000 10101011 11001101

0212:34FF:FE00:ABCD

MAC:

Binary:

Insert FFFE:

Set U/L bit::

EUI-64:

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