Performance Investigation of IPv4/IPv6 Transition Mechanisms

Performance Investigation of IPv4/IPv6 Transition Mechanisms
Performance Investigation of IPv4/IPv6
Transition Mechanisms
Jiann-Liang Chen, Yao-Chung C h a n g a n d Chien-Hsiu Lin
Department of Computer Science and Information Engineering
National Dong Hwa University
Hualien, Taiwan
E-Mail: [email protected]
Absfmcf - IPv4/1Pv6 transition always occurs process in
deploying lPv6-based services across the IPv4 Internet. The
IETF Next Generation Transition Working Group (NGtrans)
has proposed many transition mechanisms to enable the seamless
integration of IPv6 facilities into current networks. This work
mainly addresses the performance of the various tunneling
transition mechanisms used in different networks. The effect of
there mechanisms on the performance ofend-to-end applications
is explored using metrics such as transmission latency,
throughput, CPU utilization and packet loss. The measured
latency and throughput of the 6104 mechanism are better than
those ofthe configured tunnel and tunnel broker mechanisms by
8938% and 94.83%, 42.47% and 48.76%. However, the 6tc4
mechanism must work much harder (greater overhead) for each
packet sent, and it must therefore run at a higher CPU utilization
of the edge router. Larger packets had higher loss rates, for all
three tunneling mechanisms.
Keywords
- Ih.6
networks, transition mechanisms, IETF
NGtrans, tunneling mechanisms, performance
metrics.
1. Introduction
The development of the IPv6 protocol, as well as being
fundamental to the growth of Internet, is the basis of the
increase in IP functionality and performance [1,2]. The IPv6
protocol is intentionally designed to minimize impact on
layering protocols by avoiding the random addition of new
features. It will support the deployment of new applications
over the Internet, opening up a broad field of technological
development [3,4]. Companies such as Microsofr and Nokio
have issued white papers on accelerating the IPv6 process
[5,6]. Many new applications and Operation Systems,
including Windows XP and Linux Kernel 2.1.8 and over,
already integrate IPv6 support, but some major challenges
remain before an effective and smooth transition from IPv4
networks can be ensured [7].
IPv6-based networks have been implemented in isolation,
but now industry is seeking to connect these IPv6 islands over
the IPv4 ocean. Much of this work involves a return to
simplicity and ease of use with as little disruption the existing
networks as possible. Three main tiansition mechanisms have
already emerged dual stack, tunneling and translation, as
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proposed by NGtrans [SI. This work demonstrates how
tunneling mechanisms could be used to establish transparently
hybrid communications between the IPv411Pv6 worlds.
Performance issues, like transmission latency, throughput,
CPU utilization and packet loss, are also disussed.
The next section will introduce various transition
mechanisms. Section 3 addresses empirical investigation in
this testbed. Section 4 considers performance in terms of
transmission latency, throughput, CPU utilization and packet
loss. Section 5 discusses results obtained by simulating the
system.'Finally, Section 6 summarizes this work.
2. IPv4/IPv6 Transition Mechanisms
The transition between today's IPv4 Internet and the
IPv6-based Internet ofthe future will be a long process, during
which both protocols will coexist. Figure 1 shows the
transition phases. A mechanism for ensuring smooth, stepwise
and independent changeover to IPv6 services is required. Such
a mechanism must facilitate the seamless coexistence of IPv4
and IPv6 nodes during the transition period. IETF has created
the Ngtrans Group to facilitate the smooth transition from IPv4
to IPv6 services. The various transition strategies can be
broadly divided into dual stack, tunneling and translation
mechanisms [9]. These mechanisms are briefly described
below following.
Figure 1. IPv4/IpV6 Transition Phases
2.1 IPv4/IPv6 Dual-Stack Mechanism
Dual stack mechanisms literally include two protocol
stacks that operate in parallel and thus allow network nodes to
operate via either protocol IPv4 or IPv6 [IO]. They can be
implemented in both end systems and network nodes. In an
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system. they enable both IPv4 and IPv6 applications to operate
at a single node. Dual-stacked capabilities of network nodes
support the handling of both IPv4 and IPv6 packets.
In a dual-stack mechanism, specified in IETF RFC2893,
a network node includes both IPv4 and IPv6 protocol stacks in
parallel (Fig. 2) [ I I]. IPv4 applications use the IPv4 stack, and
1Pv6 applications use the 1Pv6 stack. Flow decisions are based
on the version field of IP header for receiving, and on the
destination address type for sending. The types of addresses
are usually derived from DNS lookups; the appropriate stack is
selected in response to the types of DNS records returned.
Many off-the-shelf commercial operating systems
already have dual IP protocol stacks [12]. Hence, the
dual-stack mechanism is the most extensively employed
transitioning solution. However, dual stack mechanisms
enable only similar network nodes to communicate (IPv6-IPv6
and IPv4-IPv4). Much more work is required to create a
complete solution that supports IPv6-IPv4 and IPv4-IPv6
communications.
IPv4 aPPlications
IPv6 applications
Sockets API
UDPTTCPv4
I
IPv4
1
..
UDPrTCPv6
1Pv6
LI
6. 6104Automatic Tunneling Mechanism
Automatic tunneling refers to a tunnel configuration that
does not need direct management. An automatic 6104 tunnel
enables an isolated IPv6 domain to be connected over an IPv4
network and then to a remote IPv6 networks. Such a tunnel
treats the IPv4 infrastructure as a virtual non-broadcast link, so
the IPv4 address embedded in the 1Pv6 address is used to find
the other end of the tunnel. The embedded IPv4 address can
easily be extracted and the whole IPv6 packet delivered over
the IPv4 network, encapsulated in an IPv4 packet. No
configured tunnels are required to send packets among 6104capable IPv6 sites anywhere in IPv4 Internet.
Figure 4 shows the stmcture of the 6104 address format.
The value of the prefix field (FP) is Ox00 I, which the identifies
global unicast address. The Top-Level Aggregation identifier
field (TLA) is assigned by the IANA for the 6104 mechanism.
Hence, the 1Pv6 address prefix is 2002::/16 and the 32 hits
after 2002::/16 represent the IPv4 address of the gateway
machine of the network in question. The packets thus know
the way to any other network. The 6104 mechanism is the
most widely extensively used automatic tunneling technique
[14]. It includes a mechanism for assigning an 1Pv6 address
prefix to a network node with a global IPv4 address.
6 w .Id-
ad,.*
,a,..,
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Figure 2. Dual-stacks Transition Mechanism
Figure 4.6104 Address Format
2.2 IPv4/IPv6 Tunneling Mechanisms
Tunneling, from the perspective of transitioning, enables
incompatible networks to he bridged, and is usually applied in
a point-to-point or sequential manner. Three mechanisms of
tunneling are presented- 6uver4,6lu4 automatic tunneling, and
Tunnel Broker.
A. 6over4 Mechanism
The 6over4 mechanism embeds an IPv4 address in an
IPv6 address link layer identifier part, as shown in Fig. 3 and
defines Neighbor Discovery (ND) over IPv4 using
organization-local multicast [13]. An IPv4 domain is a fully
interconnected set of IPv4 subnets, within the scope of a single
local multicast, in which at least two IPv6 nodes are present.
The 6uver4 tunneling setup provides a solution for IPv6 nodes
that are scattered throughout the base IPv4 domain without
direct IPv6 connectivity. The mechanism allows nodes, on
physical links, which are directly connected IPv6 routers to
become fully functional IPv6 nodes.
C. IpV6 Tunnel Broker
The IPv6 Tunnel Broker provides an automatic
configuration service for IPv6 over IPv4 tunnels to users
connected to the IPv4 Internet [ 151. IPv4 connectivity between
the user and the service provider is required. The service
operates as follows (Fig. 5 ) .
1. The user contacts Tunnel Broker and performs the
registration procedure.
11. The user contacts Tunnel Broker again and, following
authentication, provides configuration information (IP
address, operating system, IPv6 support software).
111. Tunnel Broker configures the network side end-point, the
DNS server and the user terminal.
IV. The tunnel is active and the user is connected to IPv6
netwnrkn.
A
.-
Figure 5. IPv6 Tunnel Broker
Figure 3.6over4 Address L i n k Layer Identifier
-
546 -
p
The basic function of translation in IPv4/IPv6
transitioning is to translate IP packets. Several translation
mechanisms are based on the SIIT (Stateless IPACMP
Translation algorithm) algorithm [16]. The SIIT algorithm is
used as a basis of the BIS (Bump In the Stack) and NAT-PT
(Network Address Translation-Protocol Translation)
mechanisms, which are described below.
network, including nodes and routers that support dual
IPv4/IPv6 stacks, were examined. T u M e h g supports early
IPv6 implementation and the use of the existing IPv4
infrastructure without changing the IPv4 modules. The
following sections describe three tunneling architectures used
for testing herein.
I
I
11
DN5.LT
FTP.\LT
-e*
I
I
I
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Figure 7. Baric NAT-PT Translalion Architecture
3.1 Confieured-tunnel Testbed
All tunneling mechanisms require that the endpoints of
the tunnel run both 1Pv4 and IPv6 networks; that is, they must
run in a dual-stack mode. Dual-stack routers run both IPv4 and
IpV6 protocols simultaneously and can thus interoperate
directly with both IPv4 and IPv6 end systems and routers.
Figure 8 shows a configured-tunnel testbed.
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R-.sr
IT-"=-l
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Figure 8. Configured-tunnel Testbed
The configured-tunnel mechanism depends on the
configuration of both end-points: one at the client site and the
other at the remote tunnel provider. Once a tunnel has been
established, the service provider will advertise the relevant
routing information to the client's network. Hence, the end
node can support a native IPvh protocol stack while the edge
router generates the tunnel and handles the encapsulation and
de-capsulation of IPv6 packets over the existing IPv4
infrastructure. Figure 9 presents the interfaces of the
dual-stack gateway.
Figure 9. Interfaces of the Dual-stack Gateway
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