分类： LINUX
2005-06-09 12:48:53
Galal Abdo Awad Murshed, Dan Komosný
Department of Telecommunications
Brno University of Technology, Faculty of Electrical Engineering and
Communications
Purkyňova 118, 612 00 Brno, Czech Republic
Abstract
The new version of Internet Protocol IPv6 (Internet Protocol Version 6) is an improved version of the Internet Protocol. The improved characteristics of IPv6 resolve and overcome many of the serious limitations of the current Internet protocol IPv4. These improved characteristics of IPv6 make the IP Internet protocol run efficiently and faster on Internet Network. This paper describes some of these characteristics and discusses the delay measurements of IPv6 and IPv4.
1 Introduction
IPv6, which is also called the next generation
Internet protocol (IPng), was recommended by the IPng Area Directions of the
Internet Engineering Task Force at the Toronto Ietf meeting on July 25,1994 in
RFC 1752 [7].
IPv4 has been working fine for a long time (about 30 years). It uses 32-bit
addresses, which provide for about 4 billion addresses (more than the world’s
population at that time).
By the late 1980s more organizations, research institutes, and universities had
connected to the Internet. The number of hosts increased dramatically in 1993
with the release of GUI (Graphical User Interface) browsers for HTML (HyperText
Markup Language). With the World Wide Web and e-mail, the number of users
continually increases and the number of free addresses of IPv4 gets lower. Also,
IPv4 cannot provide one address for each person on the earth (the number of
population is now about 6 billion). So IPv6 is designed to solve the limited
address space and other limitations of the current version of IPv4 such as
security, auto-configuration, extensibility, and peer-to-peer and mobile
applications and the like.
IPv6 has many advantages compared with the older Internet protocol IPv4. The
most useful advantages of IPv6 are address space extended from 32 bits to 128
bits, and simplified header format for efficient packet handling.
Processing packets of IPv6 by routers is easier than processing packets of IPv4,
because the hardware program knows in advance that the coming header is static
in length. Thus the packet processing speed increases.
2 IPV4/IPV6 comparison
2.1 Header comparison
The main characteristic of IPv6 is its large address space. In IPv4 there are
only 232 possible ways how to represent the address (about 4 billion
possible addresses), but in IPv6 there are 2128 possible way (about
3,4*1038 possible addresses) [2].
In the future, not only personal or network computers will need an IP address,
but also more electronic home devices will require their own unique IP
addresses. The large address space of IPv6 enables every device to obtain its
own unique Internet address. That will enable us, for example, to control the
security camera from anywhere or to turn on the air-conditioner of the house
while we are sitting in the office.
There are three types of address in IPv6: anycast, unicast and multicast [6]. In
IPv4 there are: unicast, broadcast, and multicast address.
The anycast address is an additional address to IPv6, for sending the packet to
the nearest node in the group, according to the routing protocol measure of
distance. It provides for applications such as file and print servers, DHCP,
etc. The unicast address is used to identify a single interface.
The broadcast address is undefined in IPv6, but it is one form of multicast in
IPv6.
The IPv4 address is written by dotted-decimal notation, e.g. 121.2.8.12, but
IPv6 is written in hexadecimal and consists of 8 groups, containing 4
hexadecimal digits or 8 groups of 16 bits each [6], e.g. FABC:
AC77:7834:2222:FACB:AB98:5432:4567.
The IPv6 header is a static header of 40 bytes in length, and has only 8 fields.
Option information is carried by the extension header, which is placed after the
IPv6 header. If there is no option information, there is no need for extension
header, and the packet size is thus reduced.
As shown in figure 1, the basic length of the IPv4 header comprises a minimum of
20 bytes (without option fields). The maximum total length of the IPv4 header is
60 bytes (with option fields), and it uses 13 fields to identify various control
settings.
Green: Field name kept from IPv4 to Ipv6
Blue: Field not kept in IPv6
Red: Name and position changed in IPv6
Black: New field in IPv6
Fig. 1: IPv4 Header
Fig. 2: IPv6 header
As shown in figure 1 and figure 2, the head length (IHL), identification, flag,
fragment offset, header checksum, and padding have been removed from the IPv6
header.
As shown in Figure 1, the IPv4 header has a checksum, which must be computed by
each router. It can be seen from Figure 2 that IPv6 has no header checksum
because checksums are, for example, above the TCP/IP protocol suite, and above
the Token Ring, Ethernet, etc. Removing the checksums allowed the systems to
speed up forwarding the datagrams [6]. This reduces the end-to-end delay.
A flow is the set of packets sent from one source to one or more receivers. The
two new fields in the IPv6 header are: the flow label and the priority. The flow
label (20 bits in length) is a new feature added to IPv6 to identify packets
that need special treatment by IPv6 routers. For example, it informs the router
about the amount of latency needed for video or audio streaming. In IPv6, flow
labels distinguish the traffic flow in order to optimize routing. The priority
field is used to distinguish the datagram from other datagrams. The priority
field performs priorities for two types of traffic: congestion, and
non-congestion control traffic. Non-congestion control traffic includes delay
applications [6].
As shown in Figure 2, the IPv6 header contains a 8-bit field called the Traffic
Class Field. This field allows the traffic source to identify the desired
delivery priority of its packets. The 4 bits in the priority field are divided
into two ranges. Values 0 through 7 specify the priority of traffic for which
the source is providing congestion control, values 8 through 15 specify the
priority of traffic that does not respond to congestion situations, such as
real-time traffic being sent at a constant rate.
As shown in Figure1, IPv4 contains an 8-bit field called “Service Type”. The
Service Type field is composed of a ToS (Type of Service) field and a procedure
field. The ToS field specifies the type of service and contains cost,
reliability, throughput, delay or security. The procedure field specifies the
level of priority using eight levels from 0 to 7.
2.2 Autoconfiguration
The IPv6 node has the ability of attaining dynamically its node and network
address. This ability is called Autocongifuration. There are two types of
autoconfiguration: stateful and stateless autoconfiguration [6].
Stateful autocofiguration: Both IPv6 and IPv4 use the stateful
autoconfiguration. This method uses external devices to help the node in
start-up to determine its network address, node address, and router address.
IPv6 and IPv4 use, for example, the DHCP (Dynamic Host Control Protocol) server.
Stateless autoconfiguration: IPv6 defines both a stateful and a stateless
address autoconfiguration mechanism. The stateless autoconfiguration requires no
manual configuration of hosts, minimal configuration of routers, and no
additional servers. The stateless mechanism allows a host to generate its own
addresses using a combination of locally available information and information
advertised by routers. Routers advertise prefixes that identify the subnet(s)
associated with a link, while hosts generate an "interface identifier" that
uniquely identifies an interface on a subnet. Combining the two yields an
address. In the absence of routers, a host can only generate link-local
addresses. However, link-local addresses are sufficient to allow communication
among nodes attached to the same link [15].
2.3 Routing
Routing in IPv4 is much the same as in IPv6 but the addresses are 128-bit
instead of 32-bit addresses in IPv4. The routing algorithms (OSPF - The Open
Shortest Path First, RIP - Routing Information Protocol, IDRP – Inter Domain
Routing Protocol, ISIS - Intermediate System-Intermediate System, etc.) of IPv4
can be used to route IPv6.
To support new routing functionality, IPv6 includes routing extension, which
includes [6]:
2.4 NAT and large address space
The Network Address Translation (NAT) is used in the current IPv4 Internet
protocol to expand the number of addresses. NAT [3] was a short-term solution to
IPV4 address depletion, and it presents a number of problems. NAT destroys a key
benefit of end-to-end connectivity through the network. Because of the
widespread usage of NAT in IPv4 networks, it is impossible to deploy end-to–end
security mechanisms.
In the IPv6 network with its availability of a large number of addresses for all
IP devices, there is no need for translating hundreds of Internal IP addresses
into a few global IP addresses. NAT also presents a challenge for many
applications such as IPSec (Security Protocol) and applications requiring
quality of service (QoS) such as voice over IP (VoIP). With the IPv6 protocol,
NATs are no longer necessary.
In IPv4 networks, the shortage of address space causes widespread usage of NAT.
With large address space in the IPv6 network it is possible to deploy superior
end-to-end data security mechanisms by eliminating the need for NAT.
2.5 Security
IPv6 has been designed to satisfy the growing and expanded need for network
security [3]. The first mechanism is the IP authentication Header [8], and the
second mechanism is the IP Encapsulating Security Payload [9].
IPv6 provides superior data security, which includes end-to-end support for user
authentication, data integrity and data encryption.
Security in IPv4 networks is limited to tunnelling between two networks. Also,
it is impossible to deploy end-to-end security mechanisms in many IPv4 networks,
because of the widespread use of NAT. To achieve local network security in IPv4,
the firewall or/,or filtering is used.
3 Measurements using IPv4 and IPv6 protocol
3.1 Introduction
The measurement of IP packet transmission delay and jitter is becoming
increasingly important, because these parameters are significant parameters for
the quality of service.
There are many measurement solutions designed for distributed IP traffic and
quality of service measurements such as volume, one-way-delay, jitter and packet
loss. Examples of these measurement solutions are: the METEOR Internet
Measurement Platform (IMP), Open IMP (Open Internet Measurement Project) - Open
Source Measurement Solution [4] and NLANR/AMP (National Laboratory for Applied
Network Research/Active Measurement Project).
Internet Measurement Platform (IMP) consists of: passive meters, active meters,
a data collector, and an evaluation server. The main features of IMP are [4]:
Open Internet Measurement Project (OpenIMP) consists of two passive meters
and a QoS computation server for the calculation of the delay. OpenIMP has the
following abilities [4]:
NLANR is the largest project, which is publicly available for use by network
researchers, engineers, system administrators, and students. [10].
The goal of the NLANR Measurement and Network Analysis group is to study the
operation of the high performance connection (HPC) networks, measuring the flow
of traffic and characterizing the behaviour of these networks and improving the
design by solving the problem diagnosis to deliver maximum end-to-end
performance to users.
3.2 NLANR/AMP
NLANR/AMP is collecting IPv6 performance data in a mesh of eleven active
monitors [5]. There are nine monitors in US and two are placed internationally.
Figure 3 shows the location of AMP IPv6 monitors in US. From left to right:
University of Oregon, San Diego Supercomputer Center/UCSD, University of Utah,
University of Missouri at Columbia, University of Wisconsin, Michigan
Technological University, Georgia Institute of Technology, NYSERnet, Columbia
University.
Engineers perform measurements with the aid of the AMP IPv6 project. They have
been collecting IPv6 performance data since October 2002. They have found that
the general characteristics of IPv6 paths compared with IPv4 paths is that they
incur a large base delay, a jitter, and greater loss. They believe this is an
artifact of tunnel paths that follow less-than optimal paths, underpowered
tunnel entry and exit points, and an inefficient forwarding path inside some
routers that route IPv6 natively [5].
As they replaced IPv6-in-IPv4 with native IPv6 paths, they found that the IPv6
forwarding capability of routers improved.
They collect path and delay information using the IPv4 and IPv6 versions of ping
and traceroute, and compare the data on a path-by-path basis. The data and
related graphical representations for amp-Columbia on 28 May 2004 are shown in
Table 1.
By changing the IPv6 tunnel server from a Cisco GSR router located in Kansas
City to a Juniper T640 router in Indianapolis, they found that the new path was
topologically much closer to the path followed by IPv4 packets. This results in
a substantially lower base round trip time (RTT) delay, and less jitter as shown
in Figure 6 (the red colour represents IPv4 delay and the green colour
represents IPv6 delay). Figures 4 and 5 show the path change between amp-gatech
and amp-wisc, and which components of the path changed over the course of the
day (colours represent load levels of IPv6). As shown in Figure 4 the forward
path changes markedly after the tunnel change. The reverse path (see Figure 5)
is one hop shorter after the topology change, which is the result of two hops
being replaced with one new IPv6 hop [5].
Figure 4: The forward path, []
Figure 5: The reverse path, []
|
IPv4
|
IPv6
|
IPv6 :IPv4
|
|||||||||||
|
min
|
mean
|
max
|
stddev
|
loss
|
min
|
mean
|
max
|
stddev
|
loss
|
mean
|
stddev
|
loss
|
|
|
226
|
227.14
|
247
|
2.47
|
0.00%
|
238
|
241.33
|
334
|
7.59
|
8.05%
|
1.06 : 1
|
3.07 : 1
|
-
|
|
|
181
|
183.13
|
420
|
16.84
|
0.00%
|
183
|
186.28
|
307
|
10.11
|
7.20%
|
1.02 : 1
|
1 : 0.60
|
-
|
|
|
37
|
37.00
|
38
|
0.06
|
0.00%
|
31
|
34.44
|
228
|
16.38
|
6.78%
|
1 : 0.93
|
252.24 : 1
|
-
|
|
|
47
|
47.11
|
48
|
0.32
|
0.00%
|
48
|
51.90
|
204
|
12.16
|
7.20%
|
1.10 : 1
|
38.22 : 1
|
-
|
|
|
39
|
39.57
|
42
|
0.56
|
0.00%
|
43
|
56.52
|
278
|
37.90
|
69.92%
|
1.43 : 1
|
67.72 : 1
|
-
|
|
|
53
|
53.67
|
56
|
0.58
|
0.00%
|
64
|
67.30
|
84
|
3.88
|
6.36%
|
1.25 : 1
|
6.72 : 1
|
-
|
|
|
13
|
13.67
|
21
|
0.89
|
0.00%
|
15
|
18.82
|
77
|
6.93
|
7.63%
|
1.38 : 1
|
7.80 : 1
|
-
|
|
|
80
|
87.74
|
161
|
5.84
|
0.00%
|
81
|
84.81
|
123
|
5.48
|
6.36%
|
1 : 0.97
|
1 : 0.94
|
-
|
|
|
77
|
78.22
|
105
|
3.07
|
0.00%
|
81
|
85.85
|
202
|
11.05
|
6.36%
|
1.10 : 1
|
3.60 : 1
|
-
|
|
|
55
|
56.29
|
78
|
2.13
|
0.00%
|
58
|
70.64
|
190
|
26.81
|
89.41%
|
1.25 : 1
|
12.59 : 1
|
-
|
|
|
33
|
33.74
|
35
|
0.45
|
0.00%
|
35
|
38.65
|
171
|
10.91
|
8.47%
|
1.15 : 1
|
24.40 : 1
|
-
|
|
Table 1: AMP IPv6 / IPv4 comparison for amp-Columbia []
Figure 6: Delay of IPv4 and IPv6 before and after changing the path,
[]
Conclusion
IPv6 is designed to accommodate the much greater global demand for translation
of vast real-time data of complex transmission systems and to solve problems of
the limitation of IPv4 address space. IPv6 offers a number of new features and
simplifications, which will provide additional services on the Internet.
IPv6 will have some influence on improving the general security of the Internet,
because IPv6 machines will be able to tunnel directly to each other with no need
for the virtual private network (VPN).
IPv6 will eventually replace Ipv4 and become the standard for the global
Internet. The two protocols will coexist for several years until the transition
is complete. The full transition to IPV6 will take at least a decade.
The greatest demand for new IPv6 addresses is in Asia. For example, the
population of China is more than one billion, but China has only less than 30
million IPv4 addresses available. So the large states in Asia like China and
Japan are adopting the IPv6 technology, because they need IP addresses and have
no other choice [12].
The mission of Internet measurement projects is to analyze Internet topology and
performance. They are designed, for example, to measure IP paths, collect
round-trip performance data, track persistent routing changes, and help
visualize network connectivity or provide selected IP multicast measurements for
Internet sites such as loss, delay, jitter, round trip time (RTT), packet loss,
topology, and throughput [13].
The Active Measurement Project (AMP) performs site-to-site active measurements
and analyses; it is used for detecting link congestion, catching the impact of
routing changes, and other diagnostics. It is used to detect link congestion,
catch the impact of routing changes, and other diagnostics.
The active measurements project (AMP) of NLANR/MNA (NLANR Measurement and
Network Analysis) includes IPv6 measurements [13].
Currently there are 11 Sites [SURFnet will be added shortly] that host an IPv6
AMP box for NLANR/MNA.
The site, hosting AMP IPv6 measurement endpoints, also hosts IPv4 AMP endpoints
(on the same box). NLANR/MNA can compute the relative performance of both IPv6
and IPv4. It has been found by measurement that the performance of IPv6 is
getting every day better than IPv4, partly depending on the topology of the
underlying networks.
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