1. INTRODUCTION:

In the last 20 years, the internet undertook a huge and unexpected explosion of growth [1]. There was an effort to develop a protocol that can solve problems in the current Internet protocol which is in the Internet protocol version 4 (IPv4).It was soon realized that the current internet protocol the IPv4, would be inadequate to handle the internet’s continued growth [2].The Internet Engineering Task Force was developed a new protocol in year 1990’s and it was launched IPng in 1993 which is stand for Internet Protocol Next Generation. So a new generation of the Internet Protocol (IPv6) was developed [3], allowing for millions of more IP addresses. IPv6 is an advanced version of IPv4 that support improved scalability and routing ,security and ease-of configuration, address space cardinality high-density mobility, multimedia and real time applications like Audio and Video etc[4].

IPv6 is designed to coexist with IPv4 and eventually provide better internetworking capabilities than IPv4. IPv6 offers the potential of achieving the scalability, reach ability, end-to-end internetworking, Quality of service (QoS). Due to the current scalability and complexity of the Internet IPv6 becomes mandatory. IPv6 protocol has 128-bit addresses instead 32 bit IPv4 addresses, however the migration from IPv4 to IPv6 is an instant is impossible because of the huge size of the Internet and of the great number of IPv4 users [5].One of the biggest challenges in the deployment of IPv6 is how to migrate IPv4-based infra structures to those supporting IPv6. It is impractical and costly to replace existing IPv4-based networking infra -structures with IPv6, because IPv4 is not compatible with IPv6. To ensure a flowless and successful integration of IPv6 into existing networks, the IETF IPng Transition Working Group [6] has been working on several transition strategies, tools, and mechanisms. These transition technologies play a major role in making communication between the two protocol suites. Both IPv6 and IPv4 involvement is mandatory in IPv6 transition, which leads to major security threats. The IETF Next Generation Transition Working Group (NGTrans) has proposed many transition technologies to enable the flawless integration of IPv6 facilities into current infrastructure. In general, these transition mechanisms encapsulate IPv6 packets into IPv4 packets and transport them over an IPv4 network infrastructure. The IPv6 transition mechanisms are:-

Tunneling transition mechanism, and the type of Tunneling like Automatic and Configured Tunneling, way of tunneling and IPv6 security aspect .This paper is organized as follow: In the section 2 of this paper we focus on the architecture of the IPv4 and IPv6 and the comparisons between them. Section 3 of this paper gives the detail explanation about the Tunneling Transition Mechanism and the type of the Tunneling .In section 4 we describe about the way of tunneling. Section 5 give the Overview for the Automatic and configured Tunneling in the four way of tunneling i.e. Host-to-Host, Router-to –Router, Host –to Router and vice versa. Finally in the section 6 we make some concluding remarks and discuss Future work.

1)	Dual stack
2)	Tunneling Techniques
3)	Translation.

Fig .1 The IPv6 Transition Mechanisms

2. HEADER FORMAT OF IPV4 AND IPV6:

Internet Protocol Version 4 is the current version of the which was finally introduce in 1981. It has a 32 bit address, and it supports up to 4,294,967,296 addresses. The Header Format for the IPv4 is:

Fragmentation Flags:

Removed in IPv6. Fragmentation information is not included in the IPv6 header. It is contained in a Fragment extension header. Fragment Offset: These field was removed from the IPv6. Fragmentation information is not included in the IPv6 header. It is contained in a Fragment extension header.

Version	Header Length	Service	Total Lenght
Identification			Flags	Fragment Offset
TTL	Protocol	Header Checksum
Source Address
Destination Address
Options
Options		Options

Figure 2: IPv4 Header Format Internet Protocol Version 6 is the128 bit addresses .IPv6 is designed to allow the Internet to grow steadily, both in terms of the number of hosts connected and the total amount of data traffic transmitted and it will supports unique addresses up to 340,282,366,920938,463,463,374,607,431,768,211,456.The Header Format for the IPv6 is:

Version		Traffic class	Flow label
	Payload Length		Next Header	Hop Limit
	Source Address
	Destination Address

Figure 2: IPv6 Header Format [7]

2.1 IPV6 Verses Ipv4:

This Section describes the Comparisons between the IPv4 and IPv6 Header format. These Comparisons gives the better understanding of the IPv6 then IPv4.

IPv4 Header Field Vs IPv6 Header Field:

Version:

It has same field but with different version numbers.

Internet Header Length:

This field was removed in IPv6.IPv6 does not include a Header Length field because the IPv6 header is always a fixed size of 40 bytes. Each extension header is either a fixed size or indicates its own size.

Type of Service:

It is replaced by the IPv6 Traffic Class field.

Total Length:

It was replaced by the IPv6 Payload Lengthfield, which only indicates the size of the payload.

Identification:

Removed in IPv6. Fragmentation information is not included in the IPv6 header. It is contained in a Fragment extension header.

Time to Live:

Replaced by the IPv6 Hop Limit field.

Protocol:

Replaced by the IPv6 Next Header field.

Header Checksum:

Removed in IPv6. In IPv6, bit-level error detection for the entire IPv6 packet is performed by the link layer.

Source Address:

The field is the same except that IPv6

Addresses are 128 bits in length.

Destination Address:

The field is the same except that IPv6

addresses are 128 bits in length.

Options:

Removed in IPv6. IPv4 options are replaced by IPv6

extension headers

3. Tunneling Transition Mechanism:

Tunneling is a strategy used when two computers using IPv6 want to communicate with each other and the packet must pass through a region that uses IPv4[2]. The term “tunneling” refers to a means to encapsulate one version of IP in another so the packets can be sent over a backbone that does not support the encapsulated IP version. For example, when two isolated IPv6 networks need to communicate over an IPv4 network, dual-stack routers at the network edges can be used to set up a tunnel which encapsulates the IPv6 packets within IPv4, allowing the IPv6 systems to communicate without having to upgrade the IPv4 network infrastructure that exists between the networks. This mechanism allow the node which want to use the same protocol and communicate over the network that uses another network protocol. This mechanism which is mainly used to tunnel traffic between two IPv6 hosts through an IPv4 network, or vice-versa. The Tunneling process has three basic steps i.e. Encapsulation, Decapsulation and tunneling management. it also need the two tunnel end point, generally which are dual stack IPv4/IPv6 node, to handle the encapsulation and decapsulation . In dual stack approach, they will support the both IPv4 and IPv6 at the same time. In IPv6 transition, Tunneling is commonly used for IPv6 hosts/networks to communicate with each other over IPv4 network (i.e., IPv6 over IPv4), and for IPv4 hosts/networks to communicate over IPv6 network (i.e. IPv4 over IPv6). Figure 3 show the tunneling of

Figure 3(a) .IPv6 over Ipv4 Tunneling

IPv4 Header

After Tunneling

IPv4 Header

Figure 3(b) IPv6 over Ipv4 Tunneling

In this example host and routers supporting the dual stack (i.e. dual stack node) can use tunnels to route IPv6 packets over IPv4 regions shown in the figure 3. In this example, host A sends the native IPv6 packet to router R1, which retransmits the packet in an IPv4 tunnel to router R2, which finally transmits it as a native IPv6 packet to host B. In this case, the tunnel is managed by R1 and R2. From the encapsulation point of view, implementing a tunnel means encapsulating an IPv6 packet inside an IPv4 packet, as shown in Figure 3.1. Figure 3.1 show the IPv6 header will contain addresses A and B, and the IPv4 header will contain addresses R1 and R2

3.1 TYPES OF TUNNELING MECHANISM:

IPv6 have a various Tunneling Transition Mechanism that are:

1. 1. Automatic Tunneling

2. 2. Configured Tunneling

3. 3. Tunnel Broker 4.6to 4

4. 5.6 Over 4.

In this paper we discuss about the Automatic Tunneling and configured Tunneling.

1. Automatic Tunneling:

Automatic tunneling refers to a technique where the tunnel endpoints are automatically determined by the routing infrastructure. Tunnel endpoints are determined by using a well-known IPv4 anycast address on the remote side, and embedding IPv4 address information within IPv6 addresses on the local side [10]. In this Mechanism the sender send the IPv6 packets using the IPv6 compatible address as the destination address to the receiver. When the packets enter in the boundary of IPv4 network, the router encapsulates these packets in to IPv4 packet, which should have an IPv4 address. To get this address, the router extracts the IPv4 address embedded in the IPv6 address the packet then travels the rest of its journey as an IPv4 packet.

The destination host, which is using a dual stack, now receives an IPv4 packet. Recognizing its IPv4 address, it reads the header, and finds that the packet is carrying an IPv4 packet. It then passes the packet to the IPv6 software for processing [9], [2].

Configured Tunneling:

Configured tunneling is a technique where the tunnel endpoints are configured explicitly, either by a human operator or by an automatic service known as a Tunnel Broker. Configured tunneling is usually more deterministic and easier to debug than automatic tunneling, and is therefore recommended for large, complex networks [10].Configured Tunneling is also known as explicit tunneling. In this mechanism sender sends the IPv6 packet with the receiver’s no compatible IPv6 address, however the packet cannot pass through the IPv4 region without first being encapsulated in an IPv4 packet. The two routers at the boundary of the IPv4– region are configured to pass the packet encapsulated in an IPv4 packet. The router at one end sends the IPv4 packet with its own IPv4 address as the source address and the other router’s address as the destination. The router receiver’s the packet, decapsulates the IPv6 packet, and sends it to the destination host. The destination host then receives the packet in IPv6 format and processes it [9], [2].

4. WAY OF TUNNELING:

During the transition, the tunneling can be deployed in a four way i.e. Host-to-Host, Router-to-Router, Host-to-Router and Router –to –Host.

1. 1. Host-to-Router: IPv6/IPv4 hosts can tunnel IPv6 packets to an intermediary IPv6/IPv4 router that can be reached via an IPv4 infrastructure.

2. 2. Router-to Host: IPv6/IPv4 routers can use tunnels to reach an IPv6/IPv4 host via an IPv4 infrastructure.

Figure4 (a) Host-to-Router, Router-to-Host

1. 3. Host-to-Host: IPv4/IPv6 hosts that are interconnected by an IPv4 infrastructure can tunnel IPv6 packets between themselves.

2. 4. Router-to Router: IPv6/IPv4 routers interconnected by an IPv4 infrastructure can tunnel IPv6 packets between themselves.

Figure 4(b) Host-to-Host Tunneling

5. A OVERVIEW OF THE AUTOMATIC AND CONFIGURED TUNNELING IN FOUR WAY:

In the above 1 and 4 way of tunneling methods i.e. router-to-router and host-to-router the IPv6 packet is being tunneled to a router. The endpoint of this type of tunnel is an intermediary router which must decapsulate the IPv6 packet and forwards it on to its final destination. When tunneling to a router, the endpoint of the tunnel is different from the destination of the packet being tunnelled. So the addresses in the IPv6 packet being tunneled cannot provide the IPv4 address of the tunnel endpoint. Instead, the tunnel endpoint address must be determined from configuration information on the node performing the tunneling [11].so this type of tunneling is called Configured tunneling. Configured tunnels require: Dual stack end points both IPv4 and IPv6 addresses configured at each end.

5.1 Working Process of Router-to-Router Tunneling:

(a) A packet with an IPv6 address arrives at dual stack router.

(b) Dual Stack Router A identifies its forwarding table and finds that it can route this IPv6 address by sending it to Dual Stack Router B. It finds that Dual Stack Router B’s IPv4 address is 10.1.1.1.

(d) The IPv4 cloud routes the packet using the 10.1.1.1 destination address as if it were a normal IPv4 packet. The packet finally reaches Dual Stack Router B. e) Dual Stack Router B looks at the packet and realizes that it is carrying an IPv6 packet inside. It strips out the IPv4 header and uses the IPv6 header to identify its forwarding table. It finds that it can reach the IPv6 address destination in the IPv6 network to which it is connected.

5.2 Working Process of Host-to-Router Tunneling:

(a) A packet with an IPv6 address arrives at dual stack host.

(b)It is clearly show that on one end encapsulation is taken place at the host and the other at the router; the tunnel is therefore established between the host and the router.

(d) The endpoint of this type of tunnel is an intermediary router which must decapsulate the IPv6 packet and forwards it on to

In the 2 and 3 way of tunneling methods i.e. host-to-host and router-to-host the IPv6 packet is tunnelled all the way to its final destination. In this case, the destination address of both the IPv6 packet and the encapsulating IPv4 header identify the same node. This fact can be exploited by encoding information in the IPv6 destination address that will allow the encapsulating node to determine tunnel endpoint IPv4 address automatically. Automatic tunneling employs this technique, using an special IPv6 address format with an embedded IPv4 address to allow tunneling nodes to automatically derive the tunnel endpoint IPv4 address. This eliminates the need to explicitly configure the tunnel endpoint address, greatly simplifying configuration [11].For the automatic tunneling we can use the 6 to 4, Tunnel Broker, ISATAP, Terodo, 6 over 4. For control of the tunnel paths, and to reduce the potential for tunnel relay denial-of-service attacks, manually configured tunnels can be advantageous over automatically configured tunnels.

5.3 Working Process of Host-to-Host Tunneling:

(a) In the host-to-host method, the encapsulation is done at the source host and the decapsulation is done at the destination host.

(b) The encapsulated datagram are sent through a native IPv4 Network that has no knowledge of the IPv6 network protocol [13].

(c)It is clearly shows that the both hosts having dual stack to encapsulate the packet of IPv6 in IPv4 packets and transmit over the network as an IPv4 packet utilizing all the

5.4 Working Process of Router -to-Host Tunneling:

(a) In the router-to-host tunneling configuration, an IPv6/IPv4 router creates an IPv6 over IPv4 tunnel across an IPv4 infrastructure to reach an IPv6/IPv4 node.

(b) The tunnel endpoints span the last segment of the path between the source node and destination node. The IPv6 over IPv4 tunnel between the IPv6/IPv4 router and the IPv6/IPv4 node acts as a single hop.

(c)On the IPv6/IPv4 router, a tunnel interface representing the IPv6 over IPv4 tunnel is created, and a route (typically a subnet route) is added using the tunnel interface. The IPv6/IPv4 router tunnels the IPv6 packet based on the matching subnet route, the tunnel interface, and the destination address of the IPv6/IPv4

6. CONCLUSION AND FUTURE WORK:

This paper briefly covers the Tunneling Transition Mechanism for the IPv6, these Mechanism play the important role to make the communication between IPv4 and IPv6 .This paper gives theoretical analysis about four way of automatic and configured tunneling .After analysis we find that for control of the tunnel paths, and to reduce the potential for tunnel relay denial-of-service attacks, manually configured tunnels can be advantageous over automatically configured tunnels.

Future work will be continue to analysis the various techniques about the Configured and automatic tunneling through Experimental implementation and evaluate that which tunneling transition mechanism is best.

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Received on 22.02.2013 Accepted on 15.03.2013

Research J. Science and Tech 5(3): July- Sept., 2013 page 313-318