An Examination of IPv4 and IPv6 Networks : Constraints and Various Transition Mechanisms

Jivika Govil1, Jivesh Govil2, Navkeerat Kaur3 , Harkeerat Kaur4,

Department of : Information Technology1, Electrical Engineering2, Computer Science & Engineering3, Electronics & Communication4,

Maharshi Dayanand University1, University of Michigan2, GGS Indraprastha University3&4, jivikag@email.com, jivesh@umich.edu, navkeeratkaur@yahoo.com kaurharkeerat@gmail.com

Abstract- The concept of transiting from IPv4 network to IPv6 network is being processed vigorously. Extensive study is being done presently on this subject as transition from IPv4 to IPv6 requires a high level compatibility and clear procedure for easy and independent deployment of IPv6. The transition between IPv4 internet and IPv6 will be a long process as they are two completely separate protocols. IPv6 is not backward compatible with IPv4, and IPv4 hosts and routers will not be able to deal directly with IPv6 traffic and vice-versa. In fact that there will be extreme difficulties with address allocation and routing if the internet is to continue to run indefinitely using IPv4. Also it is impossible to switch the entire internet over to IPv6 over night. As IPv4 and IPv6 will co-exist for a long time, this requires the transition and inter-operation mechanism. Due to this reason several transitions mechanisms have been developed that can be used to make the transition to IPv6 smoothly. Most applications today support IPv4 and thus there is a need to run these applications on IPv6 access network, especially to persons who are generally on mobile and they want to securely connect to their home network so as to reach IPv4 services. This paper discusses constraints, various techniques and standards require for high level compatibility smooth transition and interoperation between IPv4 and IPv6 by removing the constraints.

I. INTRODUCTION

Presently approximately 25 billion people are connected to the internet Computer networks through internet are connected worldwide and these networks are connected through routers. The task of routers is to send data between the different networks. The router together with an addressing system and transport protocol called the internet protocol IPv4 and provides a communication path between any pair of hosts. Due to paucity of address space and allocation mechanism i.e. used to allocate addresses in the internet protocol, some parts of the world are beginning to run out of addresses. A new version of internet protocol called IPv6 has been defined so as to solve the address and other problems in the currently used internet protocol. Also currently IPv4 network is suitable for stationary users, the only internet access available to mobile customer through cellular phone services running on IPv6 [1]. Implementing the transition and interoperation between IPv4 and IPv6 requires a easy process to adopt the deployment of IPv6 smoothly as Mobile IP cannot deliver IPv4 mobility from IPv6 access network. To deliver this it requires huge unnecessary investment in IPv6 infrastructure. Also we cannot move from IPv4 to IPv6 straightaway and we require developing a mechanism so that IPv4 and IPv6 exist together for atleast 20 years and during transition period IPv4 network will totally disappear [2]. This paper deals

with advantages, constraints and various transitions mechanisms from IPv4 to IPv6.

II. IPV6 OVERVIEW

IPv6 was designed to be an evolutionary step from IPv4. It was not a design goal to take a radical step away from IPv4 [3]. Functions that work in IPv4 were maintained in IPv6, and those that didn't work were removed..

A. IPv6 Features and Benefits IPv6 was designed to build on the existing features of

IPv4 and provide new services and capabilities. Listed below is an overview of several features and benefits IPv6 is intended to provide. 1) Larger Address Space – IPv6 increases the IP address size from 32 bits to 128 bits. Increasing the size of the address field increases number of unique IP addresses from approximately 4,300,000,000 (4.3×10^9) to 340,282,366, 920, 38,463,463,374,607,431,768,211,456(3.4×10^38). Increasing the address space to 128 bits provides the following additional potential benefits : a) Enhanced Applications Functionality – Simplifies direct peer-to-peer applications and networking by providing a unique address to each device. b) End-toEnd Transparency – The increased number of available addresses reduce the need to use address translation technologies c) Header Format Simplification - Some IPv4 header fields have been dropped or made optional, to reduce the common-case processing cost of packet handling and to keep the bandwidth cost of the IPv6 header as low as possible, despite the increased size of the addresses. Even though the IPv6 addresses are four times longer than the IPv4 addresses, the IPv6 header is only twice the size of the IPv4 header. d) Hierarchical Addressing – The hierarchical addressing scheme provides for address summarization and aggregation. These approaches simplify routing and manage routing table growth. e) Auto-Configuration – Users using IPv4 addresses use the Dynamic Host Configuration Protocol (DHCP) server to establish an address each time they log into a network. This address assignment process is called stateful auto-configuration. IPv6 supports a revised DHCPv6 protocol that supports stateful auto-configuration, and supports stateless auto-configuration of nodes. Stateless auto-configuration does not require a DHCP server to obtain addresses. Stateless auto-configuration uses router advertisements to create a unique address. This creates a

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“plug-and-play” environment, simplifying address management and administration. IPv6 also allows automatic address configuration and reconfiguration. This capability allows administrators to re-number network addresses without accessing all clients. Fig. – 1 illustrates the below .

Figure - 1 Auto Configuration 2) Scalability of Multicast Routing – IPv6 provides a much larger pool of multicast addresses with multiple scoping options. 3) Built in Security - Apart from the huge address, the IPv6 Internet Protocol version comes with built-in security of the source. 4) Quality-of-Service Capabilities-A new capability is added to enable the labeling of packets belonging to particular traffic "flows" for which the sender requests special handling, such as non-default quality of service or "real-time" service [4]. The phone conversations over the Internet will be smooth and clear instead of choppy and broken up like they often are now. 5) Improved Support for Options--Changes in the way IP header options are encoded allows for more efficient forwarding, less stringent limits on the length of options, and greater flexibility for introducing new options in the future. 6) Authentication and Privacy Capabilities--IPv6 includes the definition of extensions, which provide support for authentication, data integrity, and confidentiality]. This is included as a basic element of IPv6 and will be included in all implementations.

III. CONSTRAINTS OF TRANSITION PLANS FROM IPV4 TO IPV6

The actual transition process from IPv4 to IPv6 can be compared to the migration processes of smaller scale that take place all the time. Operating system and software development environment version changes are good examples of such migration. The main constraints set for the IPv6 transition should be generally the same as in any smaller scale migration. However, for the global Internet community the fulfillment of the constraints is much more important, and few shortcuts can be tolerated [5]. Followings are some of the constraints listed. 1) Incompatibility: The IPv6 designers made a fundamental conceptual mistake by designing the IPv6 address space as an alternative to the IPv4 address space, rather than an extension to the IPv4 address space. Hence a straight

forward transition plan cannot work with the current IPv6 specification. 2) Incoherence: The IPv6 designers don’t have a transition plan and due to this reason IPv4/IPv6 network has become a complex issue. Without coherent transition plan, IPv6 has no credibility. They should have designed the plan that if implemented and universally deployed will produce the magic result. 3) Distractions: Presently IPv6 address is not useful as it cannot talk to IPv4 address. If we want IPv6 to succeed as global network, we have to figure out how to make an IPv6 address just as useful as an IPv4 address . System needs to configure that every Internet computer becomes automatically enable to talk to IPv6 address. This cannot be done overnight and it is the crux of the IPv6 transition. 4) Stepwise Transition: As the transition cycle will take years and there is no way to synchronize the process on different sites. A distributed approach is necessary. Presumably only the smallest user organizations are able to switch over to IPv6 in a single step. All others must be able to make their own staged transition plan, and proceed in it with as few interdependencies as possible. IPv4 and IPv6 network equipment must be allowed to coexist and interoperate. It should even be realized that some old, small-scale systems may never be capable of running IPv6 . They will maintain the old protocol suite in the network to the end of the old hardware usage time. 5) Coexistence and Internet Working: The transition independency means that the order of migration on unique computers and network devices is not tied to the upgrade of some other systems in the network. The release dates of new computer systems, routers and application software cannot be commonly synchronized. Old equipment and software will be used in the network while the IPv6 based systems and applications are deployed. The old systems should run without modifications and be able to communicate with both the old and new systems. In practice this means a strict requirement for simultaneous support for both IPv4 and IPv6 on all new systems. 6) Feasible Address Mapping Scheme: As discussed above IPv6 brings the advantage of a very large address space where even multiple addresses can be easily reserved for each host. In addition to the complex scheme of 128-bit IPv6 address distribution, a simplified method is necessary. To make the transition process easier an optional simple mapping from an old IPv4 address is desirable . Since it is not possible to assume that all IPv4 addresses used are globally unique, the mapping may be site-specific in some cases instead of a fixed prefix. 7) IPv6 Standards and Product Evolution: Today, IPv6 technology is still evolving and this evolution is likely to continue through the federal transition period. This is as expected and is a normal evolution of the Internet standards. While the base set of IPv6 protocols are stable and mature, and product implementations are emerging, many of the standards supporting value-added IPv6 features are still evolving. Therefore, developers/organizations to be encouraged to ensure the IPv6 capabilities being procured have a viable upgrade path.

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IV. TRANSITION MECHANISMS AND INTEROPERATION

IPv6 is not backwards compatible with current internet protocol and thus it is hard to deploy as old applications will no longer work [6]. During the transition period, IPv6 nodes are going to need to communicate with IPv4 nodes and isolated “Islands of IPv6 installations” are going to need to use the wider IPv4 network to connect to each other [7]. A number of transition mechanisms have been defined and following is a brief over view of some of transition mechanism. Fig. – 2 illustrates the broadview of different transition mechanisms.

Figure – 2 Transition Mechanisms

A. Dual IP Stacks Nodes with dual IP stacks will have both IPv4 protocol

stack and an IPv6 one. When communicating with IPv6 nodes, they use IPv6 and when communicating with IPv4 nodes, they revert to IPv4. These nodes have IPv4 compatible IPv6 addresses - these are addresses where the first 96 bits of the address are zeroes and the last 32 forms a valid IPv4 address. Every current IPv4 address can be transformed to an IPv6 address in this fashion.

Consequently, this requires all dual-stack nodes to have IPv4 addresses. This may not be feasible considering that one of the major reasons for transitioning to IPv6 is that the available address space is set to run out. This approach is inefficient for routers.

Figure – 3 Dual IP Stacks Consider a LAN where all hosts are IPv6 enabled, but are

running dual IP stacks to communicate with the outside world. The entire network infrastructure, i.e. routers and

bridges etc will need to be able to deal with both protocols, maintain double routing tables, etc. [8] Simplicity of routing is supposed to be a strength of IPv6, if this sort of transition mechanism were used it would become a weakness. To get around these two problems, some mechanisms have been developed which are discussed in following paras B to F. These can be used in situations where a network has been completely converted to IPv6, but which still needs to communicate with the outside IPv4 world. They all rely on various servers or devices that sit between the IPv6 and IPv4 networks doing some form of translation. Fig. – 3 illustrates a typical dual IP Stack.

B. Dual Stack Application Level Gateway (Dual Stack ALG) Dual Stack ALG is an IP device running dual-stack and

can have access to both IPv4 and IPv6 services natively. Dual-stack servers are used as proxies to perform protocol translation with one proxy server per application (http, ftp, smtp, etc). This has the advantage that very few IPv4 addresses are required (they are only needed for the proxies), and the protocol translation step may not be such a large price to pay in situations where firewalls and proxy server already exist, which is the case in many LANs. However, the disadvantage is that Dual Stack ALG’s are not able to handle all services, particularly those that have pure end-to-end requirements.

C. Network Address Translation - Protocol Translator (NAT-PT)

NAT-PT is a dedicated hardware device residing within an IP router, situated at the boundary of an IPv4 network and an IPv6 network. By installing NAT-PT between an IPv4 and IPv6 network, all IPv4 users are given access to the IPv6 network without modification in the local IPv4-hosts (and vice versa). Equally, all hosts on the IPv6 network are given access to the IPv4 hosts without modification to the local IPv6-hosts. Further as NAT-PT device retains a pool of globally routable IPv4 addresses, which are used to assign to IPv6 nodes on a dynamic basis as sessions are initiated across the IPv6/IPv4 boundary.

Figure – 4 Network Address Translation. In addition to address translation, header translation is

performed as described in the SIIT mechanism (SIIT). As opposed to SIIT, which is a stateless translation mechanism, NAT-PT retains state via the IPv4 to IPV6 address mappings which are retained for the duration of each session. NAT-PT can be extended to NAPT-PT (Network Address Port Translation – Protocol Translation). NAPT-PT takes the address translation a stage further by enabling the translation of port numbers as well. This makes it possible to re-use one IPv4 pool address and map this one IPv4 address to many IPv5 hosts [9]. The basic NAT-PT

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translation device may additionally contain ALG’s (Application Level Gateways). ALG’s are necessary when IP addresses are embedded within the payload of an IP packet. For normal packet translation. NAT-PT would not look within the payload for IP addresses. Typical protocols that embedded IP addresses in the payload are FTP and DNS. NAT-PT requires no special configuration on the client, apart from using the correct DNS server which can be configured automatically through DHCPv6 for example.

D. Network Address Port Translation – Protocol Translation (NAPT-PT)

A large number of users, offices and telecommuting employees have multiple network nodes in their office. These are running TCP and UDP applications, but have a single IP address assigned to their remote access router by their service provider to access remote networks. The increasing number of remote access users would be gained by NAPT-PT, which allows multiple nodes in a local network, at the same time access remote networks using the single IP address assigned to their router.

NAPT-PT is a special case of dynamic NAT and NAPT-PT uses port numbers as the basics for the address translation. With NAPT-PT, IPv6 nodes are allowed to communicate with the IPv4 nodes transparently using a single IPv4 address. The TCP and the UDP ports of the IPv6 nodes are translated into the TCP and the UDP ports of the registered IPv4 addresses. This allows the TCP and the UDP ports of a number of private hosts to be multiplexed into the TCP and the UDP ports of a single external address. A pool of external addresses is used when port translation is made under NAPT-PT. The number of ports available, that is 216 = 65536, limits the number of connections per IP address. Many ports are assigned to specific services and ports up to number 1024 are well known ports.

NAPT-PT translates the source IP address, source TCP port, source UDP port and related fields such as IP, TCP, UDP and ICMP header checksums, for packets outbound from the private network. The destination IP address, destination TCP port, destination UDP port and the IP, TCP and UDP header checksums are translated, for inbound packets .

NAPT-PT solves the problem, which NAT would not be able to handle, when the pool of IPv4 addresses assigned for the translation is exhausted which implicates those newer IPv6 nodes will not be able to establish sessions with the outside world anymore .

E. Stateless IP/ICMP Translator (SIIT) SIIT (SIIT) is a transition mechanism algorithm that

translates between IPv4 and IPv6 packet headers, including ICMP, in separate translator “boxes” in the network, without requiring any per-connection state in those “boxes”. This algorithm can be used as a part of a solution that allows IPv6 hosts, which do not have a permanently assigned IPv4 address, to communicate with IPv4 only hosts [10]. NAT-PT is an example of such a solution. the RFC neither specifics how to do address assignment nor routing to and from the IPv6 hosts when they communicate with IPv4 only hosts.

F. Dual Stack Transition Mechanism, or DSTM Dual Stack host have both IPv4 and IPv6 interfaces

configure and can communicate with both IPv4 and IPv6 hosts. DSTM is an IPv4 to IPv6 transition proposal based on the use of IPv4 over IPv6 dynamic tunnels and the temporary allocation of IPv4 global addresses to Dual-Stack hosts. - DSTM is intended for IPv6-only networks in which hosts still need to exchange information with other IPv4 hosts or applications.

TABLE I PARAMETERS IN CONCERN FOR DSTM

Performance Tunnel at DSTM host on IPv6 domain allows for high scalability of IPv6-end TEP. Pays tunneling overhead of at least 40 bytes per IPv4 packet due to v4 in v6 overhead.

Scalability Since interoperability is at the edge, this is highly scalable on V6 network. Native IPv6 address prefix allows global routing scalability.

Security Good, but tunnel brokered DSTM adds even better security via Authorization, Authentication, Accounting (AAA). to determine who can set up the tunnel. ----Can use native IPv6 IPSEC only up to IPv4 tunnel TEP. ---- Can use native IPv4 IPSEC.

Cost/ Complexity

Can be offered as an enterprise service with tunnel broker & router in one box. Requires client software on hosts, but this can be distributed via DSTM tunnel broker. To reduce cost/complexity can use a DHCPv6 server, tunnel broker, or static assigned IPv4 addresses in place of DSTM address server on IPv6 domain. Administrators must set up DSTM, then tunnels can be set up and torn down automatically as needed.

TABLE II ADVANTAGES OF DSTM

Transparent to the application

All types of protocol/ applications can be forwarded transparently and no changes are needed to configure translators.

No change to legacy IPv4 application

Each host in the dominant IPv6 network will be a dual IPv4/IPv6 nodes, there are no changes required for legacy IPv4 applications. All IPv4 traffic is tunneled i.e. IPv4/IPv6, towards a DSTM Gateway.

Easy Manageability

DSTM maintains IPv6 only environment. No IPv4 routes needed. Hence easy to manage.

No Protocol Translation

As DSTM uses IPv4/IPv6 tunneling for IPv4 communications. Hence the communication is straight forward and simple.

Dynamic Allocation of IPv4 address

Whenever a DSTM client sends a request to the DSTM Server for a dynamic IPv4 address, it will be reclaimed by the server even its life time has expired. A DSTM server can serve the need of IPv4 address for a large number of IPv6 nodes by having a small IPv4 address pool.

Based on Standard Protocols

DSTM is based on Standard Protocol, hence not complex.

Security DSTM transition mechanism is more secure as it does not use NAT (Network Address Translation). SSH (Secure Shell) and IPsec with IPv4/IPv6 can be used without any modification.

The DSTM architecture is composed of an addresses server, that can provides the assignment of IPv4 addresses to IPv6 Nodes [11]. The server will also be used to maintain the mapping between the allocated IPv4 address and the permanent IPv6 address of the node. Each IPv6 DSTM will have an IPv4 interface called the Dynamic Tunneling Interface (DTI) designed to encapsulate IPv4 packets into IPv6 packets. A DSTM client on the node should be used for IPv4 address allocation and may be used to solve the

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mapping between IPv4 and IPv6 addresses. Table I provides a discussion of various parameters in respect to DSTM. Table- II highlights some of the advantages of DSTM. Also the Fig. – 5 explains the Dual Stack Transition Mechanism.

As DSTM technique provides a unique solution to the IPv4-IPv6 transition problem. This mechanism is designed to rapidly reduce the reliance on IPv4 routing and is intended for IPv6-only networks in which hosts still occasionally need to exchange information directly with other IPv4 hosts or applications. Network administration is simplified and the need of IPv4 global addresses is reduced [12].

Figure – 5. Dual Stack Mechanism

DSTM can be integrated with an IPv6 Tunnel Broker for tighter security integration. DSTM routers can be coupled with IPv4 Firewalls and Intrusion Detection systems to secure IPv4 tunnel endpoints from IPv4-based attacks. Dual Stack Transition Method (DSTM) is different than the pure Dual Stack running on a single host. Figure – 6 illustrates the same.

Figure - 6. Transition IPv6 seamlessly in DSTM

G. Dual Stack Mobile IPv4 Dual Stack Mobile IPv4 draft provides IPv6 extensions to

the Mobile IPv4 protocol. The extensions allows a node that has IPv4 and IPv6 addresses to maintain communications with either or both of its addresses while moving in IPv4 or dual stack networks. The specification essentially separates the Mobile IP signaling version from the IP version of the traffic that it tunnels [13]. Mobile IPv4 with these new extensions becomes a signalling protocol that runs over IPv4, and yet can set-up any combination of IPv4 and /or IPv6 over IPv4 tunnels. But when the user moves to an IPv6 access network this cannot be used since the signalling is sent over IPv4 only.

H. Dual Stack Mobile IPv6 The dual stack Mobile IPv6 draft provides IPv4

extensions to the Mobile IPv6 protocol . The extension allow a node that has IPv4 and IPv6 addresses to roam within the Internet using Mobile IPv6 only, while simultaneously maintaining connections using their IPv4 and IPv6 home addresses[14]. When the mobile user is located on a dual stack or IPv6 only access network, the Mobile IPv6 signalling is sent over IPv6 to the Home Agent. When the mobile user is located on an IPv4 only access network, the Mobile IPv6 signalling packets are tunneled in IPv4 to the Home Agent[15]. The drawback with the dual stack Mobile IPv6 mechanism is that it does not handle situations when only private IPv4 addresses are available in the access network, which is a common situation.

I. IPv6 over Mobile IPv4 IPv6 over Mobile IPv4 specifies a Mobile IPv4 extension

that may be used by dual stack mobile nodes to obtain IPv6 service with the use of a Mobile IPv4 registration. This extension allows for immediate deployment of IPv6 on dual stack mobile devices, without the need for a full IPv6 infrastructure. It is believed that providing IPv6 services to mobile devices in the short term will spur the growth of IPv6 networks [16]. The specification requires that the mobile node and Home Agent have dual IPv4 and IPv6 stacks, but there are no changes to the Foreign Agent and it does not need to be dual stack. Thus this mechanism with MIPv6, will achieve IPv6 mobility from any network [17].

J. IPv6-over-IPv4 Tunneling Tunneling is a mechanism that has been defined to allow

IPv6 packets to be encapsulated in IPv4 packets. A dual stack hosts can send IPv6 packets through an IPv4 tunnel to a remote IPv6 hosts without requiring an IPv6 infrastructure. Tunneling is used to carry IPv6 packets across IPv4 routed network areas. One of the requirements for tunneling is that the begin and endpoints of the tunnel are IPv6/IPv4-nodes with IPv4-compatible IPv6 addresses. Tunneling means that the whole IPv6 packet is mapped into a body of an IPv4 packet and sent across the IPv4 network area. The endpoint of the tunnel has to be either an IPv6/IPv4-header-translating-router or an IPv6/IPv4-node to de-encapsulate the packet [18]. The destination address of the new IPv4 packet is the address of the node representing the tunnel endpoint. RFC 2893 defines the following tunneling configurations with which to tunnel IPv6 traffic between IPv6/IPv4 nodes over an IPv4 infrastructure: Router-to-Router, Host-to-Router or Router-to-Host, and Host-to-Host. There are various types of tunneling.

K. Configured Tunneling Tunneling techniques are classified by way the

encapsulating node determines the address of the node at the end of the tunnel. In router-to-router and host-to-router tunneling methods, the IPv6 packet is tunneled to a router. The tunnel endpoint is an intermediary router. The intermediary router decapsulates the IPv6 packet, then forwards it to its final destination. When tunneling to a router, the tunnel endpoint differs from the tunneled packet’s destination. So the addresses in the tunneled IPv6

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packet do not provide the IPv4 address of the tunnel endpoint. Instead, the node performing the tunneling provides configuration information that determines the tunnel endpoint address [19]. This type of tunneling is called “configured tunneling.” (Fig. – 7)

Figure -7 Configured Tunneling

L. Automatic Tunneling In the host-to-host and router-to-host tunneling methods,

the IPv6 packet is tunneled all the way to its final destination. The tunnel endpoint is the node to which the IPv6 packet is addressed. Because the tunnel endpoint is the IPv6 packet’s destination, the IPv6 packet’s destination address determines the tunnel endpoint: if that address is an IPv4-compatible IPv6 address, then the low-order 32-bits hold the destination node’s IPv4 address. That can be used as the tunnel endpoint address. This technique avoids the need to explicitly configure the tunnel endpoint address. Deriving the tunnel endpoint address from the embedded IPv4 address of the packet’s IPv6 address is called “automatic tunneling.” (Fig. – 8)

Figure -8 Automatic Tunneling

M. ISATAP Tunnels Intra-Site Automatic Tunnel Addressing Protocol

(ISATAP) is another tunneling technique (Fig. - 9). It differs from manually configured tunneling in that ISATAP tunnels are automatically defined rather than statically defined. Also, ISATAP tunnels are primarily used between hosts and routers, whereas manually configured tunnels are used between routers. With ISATAP, a tunnel is created from a host, such as a PC, to a router or Layer 3 switch. The tunnel is established by using the IPv4 addresses of both the host and the router. The tunnel is “automatic” in that the

host establishes the tunnel only when it needs to; the host is also able to discover the tunnel destination (that is, the router’s IPv4 address) dynamically through DNS or a local definition. Because both IPv4 and tunneled IPv6 packets are transported over a single common IPv4 infrastructure, IPv4-dependent applications can continue to use IPv4 while newer IPv6-capable applications can be deployed immediately.

Figure -9 ISATAP Tunnels

As a transition strategy, ISATAP is ideal for campus and branch sites because ISATAP allows organizations to activate IPv6 connectivity on the existing IPv4-only network while the infrastructure is gradually migrated to integrate native IPv6 capabilities. Thus, the immediate effect on the IPv4 support infrastructure is reduced to the configuration of one ISATAP router, but it is recommended that at least two ISATAP routers to be deployed for high availability. Additionally, because ISATAP allows native IPv6 connectivity to be activated first in the backbone, other parts of the IPv4 infrastructure can preserve their investment as they naturally evolve to support IPv6.

Figure -10 An Example ISATAP Configuration

ISATAP islands can also be created to allow gradual evolution to native IPv6 capabilities within different parts of the organization without blocking end-to-end IPv6 service deployments. Although it has many benefits, ISATAP does not support IPv6 multicast, so this would not be the most appropriate transition strategy for organizations requiring that capability. Fig. – 10 is an example of

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ISATAP configuration and Fig. – 11 shows an ISATAP Router.

Figure -11 An ISATAP Router

N. 6 to 4 This is an IETF standard and specified in RFC 305. When

one IPv6 network connects to other IPv6 network this mechanism is used because it connects IPv6 end–site networks by automatic tunneling over the intervening IPv4 internet. A special IPv6 routing prefix is used to indicate that the remaining 32-bits of the external routing prefix contains the IPv4 end-point address of a boundary IPv6 router for the site, that will respond to IPv6 in IPv4 encapsulation. This will allow a host that is located behind a 6 to 4 router to communicate the other 6 to 4 hosts on the Internet. When the host sends an IPv6 packet to another 6 to 4 host, the packet is tunneled in IPv4 at the 6 to 4 router using the IPv4 address contained in the prefix of the 6 to 4 destination address as the IPv4 destination address. At the destination site the IPv4 header is removed at the 6 to 4 boundary router and forwarded to the appropriate 6 to 4 host by using the IPv6 routing infrastructure of the destination site [20]. In other words by using a 6 to 4 replay router, a 6 to 4 host can send IPv6 packets to a native IPv6 node on the IPv6 Internet. The packets are encapsulated in IPv4 at the 6 to 4 router and sent to the IPv4 address of the configured 6 to 4 relay router.

Figure – 12. 6 to 4 site

The relay router has native connectivity to the IPv4 and IPv6 Internet. The 6 to 4 router removes the IPv4 header and forwards the IPv6 packet to the appropriate IPv6 Internet host. So these two pieces of information are required i.e. a) Outside visible address (this might be a gateway or similar) from which we drive our IPv4 48 bit prefix and then somehow choose the rest of the address. b)

The address of 6 to 4 gateway to use, to connect to the rest of the IPv6 world. Fig. 12 shows a typical 6 to 4 site and Fig. – 13 shows 6 to 4 components.

Figure – 13. 6 to 4 components

O. 6 over 4 6 over 4, also known as IPv4 multicast tunneling, is a

host-to-host, host-to-router, and router-to-host automatic tunneling technology that is used to provide unicast and multicast IPv6 connectivity between IPv6 nodes across an IPv4 intranet. 6 over 4 hosts use a valid 64-bit prefix for unicast addresses and the interface identifier :WWXX:YYZZ, where WWXX:YYZZ is the colon-hexadecimal representation of the IPv4 address (w.x.y.z) assigned to the host. By default, 6 over 4 hosts automatically configure the link-local address FE80::WWXX:YYZZ on each 6 over 4 interface.

6 over 4 treat an IPv4 infrastructure as a single link with multicast capabilities. This means that Neighbor Discovery processes (such as address resolution and router discovery) work as they do over a physical link with multicast capabilities. To emulate a multicast-capable link, the IPv4 infrastructure must be IPv4 multicast-enabled. IPv4 multicast is not generally available on all networks, and there are scalability issues with this approach. It is ideal for small self contained networks where multicasting is available.

P. Bump-In-the-Stack (BIS) Mechanism The BIS mechanism is for communication between IPv4

applications on an IPv4-only host and IPv6-only hosts. The mechanism is a solution for users who cannot upgrade their certain application for some reasons after all applications are modified. So BIS is not a mechanism that is designated for the initial stage in the transition from IPv4 to IPv6, but it’s probably a mechanism that will be used in the future to connect the ’old’-legacy IPv4 applications with the widely use of IPv6 applications [21].

Three extra layers - name resolver extension, address mapper, and translator - are added to the IPv4 protocol stack between the application and network layers. Whenever an application needs to communicate with an IPv6-only host, the extra layers map an IPv6 address into the IPv4 address of the IPv4 host.

BIS mechanism has some limitations. BIS performs the translation of IPv4 packets to IPv6. This gives an IPv6 host

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the ability to use the translated IPv6 packets. The translation cannot be applied to IPv4 applications, which use the IPv4 option header, since it is impossible to translate IPv4 option headers to IPv6, and IPv6 option headers to IPv4 [22]. Only fragmentation and routing headers have the exception to be translated. Another limitation of BIS is that the extension name resolver cannot handle the secure DNS protocol. Further the BIS mechanism works only with unicast communication, and does not support multicast communication.

Q. Bump-In-The-API (BIA) Mechanism BIA Mechanism inserts an API Translator between the

socket API module and the TCP/IP module in the dual stack hosts, to translate the IPv4 socket API function to IPv6 socket API function and vice versa. Thus transition is simplified without IP header translation. When using BIA, the dual stack host assumes that there exists both IPv4 and IPv6 stacks on the local node. When an application on the dual stack communicate with other IPv6 hosts, the API translator detects the socket API functions from IPv4 applications and invokes the IPv6 socket. API functions to communicate with the IPv6 hosts, and vice versa. In order to support communication between IPv4 applications and the target IPv6 hosts, pooled IPv4 addresses will be assigned through the name resolver in the API translator.

R. Transport Relay Translator (TRT) The transport relay translator (TRT) mechanism functions

on the transport layer of the TCP/IP reference model. It allows IPv6-only nodes to communicate with IPv4-only nodes by translating TCP-over-IPv6 to TCP-over-IPv4, and the other way round. The TRT mechanism works the same for UDP traffic. The TRT system can be located on a dual stack host or router. - When an initiating IPv6 host wants to communicate with an IPv4 host it needs an IPv6 destination address? All TCP traffic from the IPv6 host goes through the TRT system, which functions as a traffic relay server. When the TRT system receives incoming TCP traffic from an IPv6 source host (X6) to an IPv4 destination host (Y4), it makes an IPv6 connection with the initiating IPv6 host. The TRT system is configured with a dummy IPv6 prefix like C6::Y4/64, where Y4 is the destination IPv4 address. The initiating IPv6 host has the ability to connect to the IPv4 host through the IPv6 address C6::Y4. After that, the relay server makes a connection with the IPv4 host and forwards the TCP traffic to the IPv4 host. When the relay server receives traffic from the IPv4 host, it establish in the same way a virtual connection with address C6::/64, and forwards the traffic to the IPv6 host.

S. SOCKS-Based IPv6/IPv4 Gateway The SOCKS-based IPv6/IPv4 gateway mechanism is for

communication between IPv4-only and IPv6-only hosts. It consists of additional functionality in both the end system (client) and the dual-stack router (gateway) to permit a communications environment that relays two terminated IPv4 and IPv6 connections at the application layer. This mechanism is based on the SOCKSv5 protocol, and inherits all the features of that protocol. Existing SOCKSv5 commands are unchanged, and the protocol maintains the

end-to-end security between the client and the gateway, and the gateway and the destination. The mechanism uses a feature called DNS Name Resolving Delegation to determine IPv6 addresses, delegating the name resolving to the gateway, thus requiring no change to existing DNSs.

V. CONCLUSION

IPv6 solves internet scaling challenges, provides flexible transition mechanisms for the current internet, and meets the needs of such new markets as mobile, personal computing devices, network entertainment and device control. Thus we must implement IPv6 as early as possible. Till today no single best solution for transition plan is developed though there are large set of IPv6 transition tools available. This transition plans are likely to be site specific. We must gain the experience in IPv6 operation as early as possible and must work towards only adopting IPv6 networks.

REFERENCES [1] C. Perkins, “IPv6 from the Viewpoint of Mobile Wireless,” The

COOK Report on Internet, Vol. IX No.11, February 2001. [2] WIDE project. SHISA, 2006. http://www.mobileip.jp/. [3] WIDE project, 2006. http://www.wide.ad.jp/. [4] Nautilus6 project. MonNemo: A NEMO Monitoring Application,

2006.http://software.nautilus6.org/. [5] Nautilus6 Project, 2006. http://www.nautilus6.org/. [6] “Interoperability between IPv4 and IPv6.”

(http:/ntrg.cs.tcd.ie/undergrad/ 4ba2.02/ipv6/interop.html [7] K. K., Ettikan, et al. “Application Performance Analysis in Transition

Mechanism from IPv4 to IPv6,” Multimedia University (MMU), Jalan Multimedia, June 2001.

[8] S. Shepler, B. Callaghan, D. Robinson, R. Thurlow, C. Beame, M. Eisler, D. Noveck, “Network File System Version 4 Protocol,” RFC 3530, April 2003.

[9] G. Tsirtsis, P. Srisuresh, “Network Address Translation - Protocol Translation (NAT-PT),” Internet Engineering Task Force, February 2000.

[10] E.Nordmark, “Stateless IP/ICMP Translation Algorthism (SIIT),” RFC 2765, February 2000.

[11] V. Devarapalli, R. Wakikawa, A. Petrescu, and P. Thubert, “Network Mobility (NEMO) Basic Support Protocol,” Technical Report RFC3963, IETF, January 2005.

[12] B. Carpentere K. Moore, “Connection of IPv6 Domains via IPv4 Clouds,” RFC3056, Feb. 2001.

[13] G. Tsirtsis, H. Soliman, “Dual Stack Mobile IPv4,” draft.tsirtsis-v4v6- mipv4-00 txt, August 2003.

[14] H. Soliman, G. Tsirtsis, V. Deverapalli, J. Kempf, H. Levkowetz, P. Thubert, and R. Wakikawa, “Dual Stack Mobile IPv6 (DSMIPv6) for Hosts and Routers,” Technical Report draft-ietf-mip6-nemo-v4traversal-01, IETF, March 2006.

[15] D. Johnson, C. Perkins, J. Arkko, “Mobility Support in IPv6,” draft-ietfmobileip- ipv6-24-txt. June 2003.

[16] D.B. Green, “DoD IPv6 Standards Profiles for IPv6 Capable Products,” Version 1, The First Thailand IPv6 summit May 2006. http://www.tahilandipv6.net/ipv6summit/ en/home/index.html.

[17] P. R. Calhoun, P. E. Engelstad, T. Hiller, P. J. McCann, “IPv6 over Mobile IPv4,” draft-mecann-mobileip-ipvvmipv4-03.txt., October 2002.

[18] L. David, Mills, “Network Time Protocol (Version 3) Specification, Implementation and Analysis,” RFC 1305, March 2002.

[19] A. Durand, P. Fasano, I. Guardini, D. Lento, “IPv6 Tunnel Broker,” Internet Engineering Task Force, January 2001.

[20] Jivesh Govil, Jivika Govil, “On the Investigation of Transactional and Interoperability Issues between IPv4 and IPv6”, 2007 IEEE Electro/Information Technology Conference, (EIT 2007) 17-20 May 2007, Chicago,USA

[21] I. Raicu, “An Empirical Analysis of Internet Protocol version 6 (IPv6),” Master Thesis, Wayne State University, 2002.

[22] S. Lee, M.K. Shin, Y.J. Kim, E. Nordmark, A. Dorant, “Dual Stack Hosts Using Bump-in-the-API,” (BIA), RFC 3338, October 2002.

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