Establishing Link between IPv6 Networks Using IPv4 Clouds

Transcription

1 International Journal of Video & Image Processing and Network Security IJVIPNS-IJENS Vol: 11 No: 03 5 Establishing Link between IPv6 Networks Using IPv4 Clouds 1 Junaid Qayyum, 2 Fayyaz Gul 1,2 Gandhara University of Sciences Peshawar, 25000, Pakistan Junaidkhan2311@ymail.com fayyaz_gul87@live.com ABSTRACT Migrating from IPv4 to IPv6 in an instant is impossible because of the huge size of the Internet and of the great number of IPv4 users. Moreover, many organizations are becoming more and more dependent on the Internet for their daily work, and they therefore cannot tolerate downtime for the replacement of the IP protocol. As a result, there will not be one special day on which IPv4 will be turned off and IPv6 turned on because the two protocols can coexist without any problems. The migration from IPv4 to IPv6 must be implemented node by node by using auto configuration procedures to eliminate the need to configure IPv6 hosts manually. This way, users can immediately benefit from the many advantages of IPv6 while maintaining the possibility of communicating with IPv4 users or peripherals. Consequently, there is no reason to delay updating to IPv6! This paper synopsises describes IPV6, Features, Benefits, Tunneling and the consequently solution for establishing link between IPV6 and IPV4. 1. INTRODUCTION Internet Protocol version 4 (IPv4) is the fourth iteration of the Internet Protocol (IP) is the basis of the TCP/IP communication protocols used to transport data, voice and video packets over the Internet. Internet Protocol version 6 (IPv6) is the next-generation network protocol, which has been standardized to replace the current IPv4. It holds great promise to become the backbone of the future of the Internet and offers a significant improvement over IPv4 in terms of scalability, security, mobility and convergence. The basic framework of the IPv6 protocol was standardized by the Internet Engineering Task Force (IETF) in the 1990s. However, there is still ongoing development of certain advanced aspects of the protocol. [1] Although the Internet Protocol IPv4 was giving efficient service over than 20 years, but the new Internet Protocol IPv6 provides higher efficiency like having enough level of IPs, stronger security and mobility. In fact it is good to evaluate the performance benefits that we can get from IPv6 protocol in compare to the IPv4 protocol. We can upgrade the existing IPv4 infrastructure to the next generation Internet Protocol (IPv6) and get its advantages using the transition mechanisms. 2. WHY IPV6? Address depletion has been the primary driver behind the need for IPv6, but it is also driven by the demand for wireless devices, which, because

2 International Journal of Video & Image Processing and Network Security IJVIPNS-IJENS Vol: 11 No: 03 6 they access the Internet, require their own IP addresses. The explosion in the use of handheld wireless devices is evidenced by their predicted shipment numbers, which is expected to grow from 430m in 2002 to 760m in 2006, and mobile internet users are expected to exceed 1.2 billion before the end of the decade. The increasing number of Internet users, systems, and the convergence of services into common infrastructure will drive the demand for IPv6. The commercial opportunities that IPv6 can provide for wireless devices, peer-to-peer networking and the smart home are also driving the move to the new technology. The wireless market requires a low latency, always on, auto-roaming alwaysreachable IP service. Peer-to-peer networking enables a group of computers to communicate directly with each other, rather than through a central server, in order to avoid the expense and delay of handling all the traffic on a server. Peer-to-peer networking is used for multiplayer online games, IPtelephony, video-conferencing and new business models similar to Napster. In addition, other Commercial opportunities for smart home products, such as Internet enabled automobiles, security systems and kitchen appliances are also pushing the transition to IPv6. In some countries, the pressures associated with address depletion, combined with these commercial opportunities, have resulted in governments mandating the move to IPv6.The European Commission as well as the Japanese, Taiwanese and Korean governments have mandated the move and other Asian countries are working towards it. The United States has been somewhat slower to take up IPv6, although the US Department of Defense has indicated it aims to complete it s by [2] 3. BENEFITS FROM IPV6 The new features of IPv6 result in a number of business benefits: Lower network administration costs: The autoconfiguration and hierarchical addressing features of IPv6 will make networks easy to manage. Optimized for next-generation networks: Getting rid of NAT re-enables the peer-to-peer model and helps with deploying new applications (e.g., communications and mobility solutions, such as VoIP.) [3] Protection of company assets: Integrated IP security (IPsec) makes IPv6 inherently secure and provides for a unified security strategy for the entire network. Investment protection: The transition and translation suite of protocols helps with easy and planned migration from IPv4 and IPv6, while allowing for coexistence in the transition phase. 4. IPV6 ADDRESSING The architecture, hierarchical addressing, auto configuration and packet headers distinguish IPv6 addresses from IPv4 addresses. 4.1 ARCHITECTURE IPv6 increases the IP address space from 32 bits to 128 bits. The new 128-bit IPv6 addresses are represented in the form of eight 16 bit components divided by colons, i.e., x:x:x:x:x:x:x:x. Hexadecimal notation, rather than familiar dotted decimal notation, is usually used to write IPv6 addresses, as shown in the following example: FE80:0000:0000:0000:0260:97FF:FE8F:64AA 4.2 HIERARCHICAL ADDRESSING The IPv6 hierarchical address architecture was designed to support hierarchical routing, which allows smaller routing tables and more efficient address allocation. [4] Smaller routing tables increase routing efficiency and provide faster routing, through faster route lookup and reduced latency. With IPv6, aggregation is achieved by providing an address prefix and the organization of addresses into two levels public topology and interface identifier. Public topology relates to providers of public Internet services and the interface identifier relates to specific interfaces on a link. In IPv4, blocks of addresses are

3 International Journal of Video & Image Processing and Network Security IJVIPNS-IJENS Vol: 11 No: 03 7 preassigned in a non hierarchical manner. As a consequence, many addresses still remain unused although classless inter-domain routing has, to some extent, lessened this issue. The IPv6 solution is more effective because the higher order levels sub-divide their addresses, as required, to efficiently provide the lower levels with their addresses. 4.3 AUTO-CONFIGURATION Unlike IPv4, IPv6 does not require the IP address of a host, network mask and default gateway to be configured manually by an administrator. IPv6 enables address auto-configuration of hosts, not only providing network configuration efficiencies but also enabling mobile devices to automatically connect to the Internet. In IPv6, autoconfiguration can be performed either through a stateless or a stateful address auto-configuration. If the network does not require the use of any specific addresses, only that the addresses be unique and routable, stateless address autoconfiguration is suitable. Stateless address autoconfiguration is done through router advertisements. IPv6 hosts generate their own addresses by combining their interface identifiers7 with the IPv6 prefix(es) advertised by routers. This enables an administrator to simply configure the router to advertise IPv6 prefixes and all devices connected to the router will automatically have their addresses configured. Even without a router, IPv6 devices on the same link can communicate with each other because they have automatically generated link-local addresses, which are derived from their Media Access Control (MAC) addresses. Stateful auto-configuration involves obtaining all required addresses and configuration information from a server and is usually used when stateless configuration fails or is inadequate. Stateful address configuration is achieved through the use of Dynamic Host Configuration Protocol version 6 (DHCPv6). DHCPv6 enables the management and dynamic configuration of addresses from a server and prefix delegation. Prefix delegation allows a router at a customer s premises to request an IPv6 prefix to be used on their site. Prefix delegation combined with router advertisements enable addresses to be automatically configured on all devices in a network. 4.4 IPV6 HEADER IPv6 simplifies the address header information so the processing of IP packets is less complicated than in IPv4. IPv6 allows for header compression and optional header extensions as well as providing Quality of Service (QoS) or content prioritization features that improve performance over IPv4. No longer contains the header length, identification, flags, fragment offset and checksum in the base header, some of which now occur elsewhere, like in the extension headers. Is a fixed length of 40 bytes and extension headers can be concatenated after the IPv6 header. Uses a hop limit instead of a time to live field. Provides integrated QoS support through the traffic class field, which replaces the type of service field, and the flow label field.

4 International Journal of Video & Image Processing and Network Security IJVIPNS-IJENS Vol: 11 No: IPV6 BACKBONE NETWORK TOPLOGY The IPv6 Group is a part of the State Key Laboratory of Software Development Environment (SKLSDE) in BUAA, China. We took up with research on IPv6 backbone network topology discovery, modeling and analysis. Dolphin is our IPv6 backbone network topology discovery system, based on asynchronous traceroute probe. With the help of Dolphin, we are able to obtain some topological information of the IPv6 backbone network. Until :00, we have found 1214 ASes. Kinds of visualization tools we developed facilitate the display of topological information and analytical findings. Based on the data collected, we also established IPv6 internet network model to interpret the new metrics of IPv6 internet network topology. And at the same time, we presented some new algorithms in complex network analysis. Our future work includes measurements on the links, analysis of complex network robustness. The following pictures display our recent IPv6 backbone topology discovery and display results.

5 International Journal of Video & Image Processing and Network Security IJVIPNS-IJENS Vol: 11 No: IPv4 vs IPv6 IPV4 Source and destination addresses are 32 bits (4 bytes) in length. IPSec support is optional. IPv4 header does not identify packet flow for QoS handling by routers. Both routers and the sending host fragment packets. Header includes a checksum. Header includes options. Address Resolution Protocol (ARP) uses broadcast ARP Request frames to resolve an IP address to a link-layer address. Internet Group Management Protocol (IGMP) manages membership in local subnet groups. ICMP Router Discovery is used to determine the IPv4 address of the best default gateway, and it is optional. Broadcast addresses are used to send traffic to all nodes on a subnet. Must be configured either manually or through DHCP. Uses host address (A) resource records in Domain Name System (DNS) to map host names to IPv4 addresses. Uses pointer (PTR) resource records in the IN-ADDR.ARPA DNS domain to map IPv4 addresses to host names. Must support a 576-byte packet size (possibly fragmented). IPV6 Source and destination addresses are 128 bits (16 bytes) in length. IPSec support is required. IPv6 header contains Flow Label field, which identifies packet flow for QoS handling by router. Only the sending host fragments packets; routers do not. Header does not include a checksum. All optional data is moved to IPv6 extension headers. Multicast Neighbor Solicitation messages resolve IP addresses to link-layer addresses. Multicast Listener Discovery (MLD) messages manage membership in local subnet groups. ICMPv6 Router Solicitation and Router Advertisement messages are used to determine the IP address of the best default gateway, and they are required. IPv6 uses a link-local scope all-nodes multicast address. Does not require manual configuration or DHCP. Uses host address (AAAA) resource records in DNS to map host names to IPv6 addresses. Uses pointer (PTR) resource records in the IP6.ARPA DNS domain to map IPv6 addresses to host names. Must support a 1280-byte packet size (without fragmentation).

6 International Journal of Video & Image Processing and Network Security IJVIPNS-IJENS Vol: 11 No: IPV4/IPV6 TRANSITIONS MECHANISMS Of major importance during the development of IPv6 has been how to do the transition away from IPv4, and towards IPv6. The work on transition Strategies, tools, and mechanisms have been part of the basic IPv6 design effort from the beginning. The current transition efforts, taking place at the IETF IPng Transition Working Group (Ngtrans), will continue until it is clear that the transition will be successful. These transition design efforts resulted in a basic Transition Mechanisms Specification for IPv6 hosts and routers that specifies the use of a Dual IP layer providing complete support for both IPv4 and IPv6 in hosts and routers, and IPv6-over-IPv4 tunneling, encapsulating IPv6 packets within IPv4 headers to carry them over IPv4 routing infrastructures.ietf has created the Ngtrans Group to facilitate the smooth transition from IPv4 to IPv6 services. [5] The various transition strategies can be broadly divided into three categories, including dual stack, tunneling and translation Mechanism. [6] 7.1 IPV4/IPV6 DUAL-STACK MECHANISM Dual-stack mechanisms include two protocol stacks that operate in parallel and allow network nodes to communicate either via IPv4 or IPv6 [7]. They can be implemented in both end system and network node. In end systems, they enable both IPv4 and IPv6 applications to operate at the same time. The Dual-stack capabilities of network nodes support the transport of both IPv4 and IPv6 packets. In the dual-stack mechanism, specified in IETF RFC2893, a network node includes both IPv4 and IPv6 protocol stacks in parallel [8].

7 International Journal of Video & Image Processing and Network Security IJVIPNS-IJENS Vol: 11 No: IPv4 applications use the IPv4 stack, and IPv6 applications use the IPv6 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 [9]. Hence, the dual-stack mechanism is the most extensively employed transition solution. However, dual stack mechanisms enable only similar network nodes to communicate with each other (IPv6-IPv6 and IPv4-IPv4). Much more works are required to create a complete solution that supports IPv6-IPv4 and IPv4-IPv6 communicatins communications. 7.2 IPV4/IPV6 TUNNELING MECHANISMS Tunneling, from the perspective of transitioning, enables incompatible networks to be bridged, and is usually applied in a point-to-point or sequential manner. Three mechanisms of tunneling are presented: IPv6 over IPv4, IPv6 to IPv4 automatic tunneling, and Tunnel Broker IPV6 OVER IPV4 MECHANISM The IPv6 over IPv4 mechanism embeds an IPv4 address in an IPv6 address link layer identifier part, and defines Neighbor Discovery (ND) over IPv4 using organization-local multicast [10]. 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 IPv6 over IPv4 tunneling setup provides a solution for IPv6 nodes that are scattered throughout the base IPV6 TO IPV4 AUTOMATIC TUNNELING MECHANISM Automatic tunneling refers to a tunnel configuration that does not need direct management. An automatic IPv6 to IPv4 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 nonbroadcast link, so the IPv4 address embedded in the IPv6 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 6to4- capable IPv6 sites anywhere in IPv4 Internet. The 6to4 mechanism is the most widely extensively used automatic tunneling technique [11]. It includes a mechanism for assigning an IPv6 address prefix to a network node with a global IPv4 address IPV6 TUNNEL BROKER The IPv6 Tunnel Broker provides an automatic configuration service for IPv6 over IPv4 tunnels to users connected to the IPv4 Internet [12]. IPv4 connectivity between the user and the service provider is required. The service operates as follows. I. The user contacts Tunnel Broker and performs the registration procedure. II. The user contacts Tunnel Broker again for authentication and providing configuration information (IP address, operating system, IPv6 support software, etc.). III. 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 networks.

8 International Journal of Video & Image Processing and Network Security IJVIPNS-IJENS Vol: 11 No: IPV4/IPV6 TRANSLATION MECHANISM The basic function of translation in IPv4/IPv6 transition is to translate IP packets. Several translation mechanisms are based on the SIIT (Stateless IP/ICMP Translation algorithm) algorithm [13]. The SIIT algorithm is used as a basis of the BIS (Bump In the Stack) and NAT- PT (Network Address Translation-Protocol Translation) mechanisms BUMP-IN-STACK-MECHANISM BIS mechanism (RFC 2767) includes a TCP/IPv4 protocol module and a translator module, which consists of three bump components and is layered above an IPv6 module [14]. Packets from IPv4 applications flow into the TCP/IPv4 protocol module. The identified packets are translated into IPv6 packets and then forwarded to the IPv6 protocol module. The three bump components are the extension name resolver, which examines DNS lookups to determine whether the peer node is IPv6-only; the address mapper, which allocates a temporary IPv4 address to the IPv6 peer and caches the address mapping; and the translator, which translates packets between IPv4 and IPv6 protocol. snoop packet payloads, and the application may therefore be unaware of it. Hence, the NAT-PT mechanism depends on ALG agents that allow an IPv6 node to communicate with an IPv4 node and vice versa for specific applications. The NAT-PT mechanism is an interoperability solution that needs no modification or extra software, such as dual stacks, to be installed on any of the end user nodes, either the IPv4 or the IPv6 network. This mechanism implements the required interoperability functions within the core network, making interoperability between nodes easier to manage and faster to manifest NETWORK ADDRESS TRANSLATION-PROTOCOL TRANSLATION The NAT-PT mechanism is a stateful IPv4/IPv6 translator [15] [16]. NAT-PT nodes are at the boundary between IPv6 and IPv4 networks. Each node maintains a pool of globally routable IPv4 addresses, which are dynamically assigned to IPv6 nodes when sessions are initiated across the IPv6/IPv4 boundary. This mechanism allows native IPv6 nodes and applications to communicate with native IPv4 nodes and applications, and vice versa. The NAT-PT translation architecture also include one or more ALGs (Application Level Gateways). The basic NAT-PT function does not

9 International Journal of Video & Image Processing and Network Security IJVIPNS-IJENS Vol: 11 No: SOLUTION: ESTABLISHING LINK BETWEEN IPV4 & IPV6 USING TUNNELING MECHANISM Our Lab is between Router to Router. A tunnel is configured between Cisco routers by creating tunnel interface in the routers that border the IPv6 and IPv4 networks. IPv6 subnets are defined on both side and IPv6 dynamic protocol is in used RIPng, BGP or OSPFv3, in our lab. We used RIPng. A tunnel is configured between these two IPv6 enable routers to communicate through IPv4 cloud. I took just two 7200 series router and performed this lab. So here are the steps and configuration of the Lab. Router_A (config) # ipv6 unicast-routing Router_A (config) # interface serial 1/0 Router_A (config) # ip address Router_A (config) # no shutdown Router_A (config) # keepalive Router_A (config) # clock rate Router_A (config) # interface FastEthernet 0/0 Router_A (config) # ipv6 enable Router_A (config) # ipv6 address 2001:0:0:1:: 1/64 Router_A (config) # ipv6 rip 1 enable Now to define Tunnel Interface on Router_A Router_A (config) # interface Tunnel 0 Router_A (config) # ipv6 address 2001:0:0:5:: 1/64 Router_A (config) # tunnel source serial 1/0 Router_A (config) # tunnel destination Router_A (config) # tunnel mode ipv6ip Router_A (config) # ipv6 rip 1 enable Now the configurations on the other side are as under

10 International Journal of Video & Image Processing and Network Security IJVIPNS-IJENS Vol: 11 No: Router_B (config) # ipv6 unicast-routing Router_B (config) # interface serial 1/0 Router_B (config) # ip address Router_B (config) # no shutdown Router_B (config) # keepalive Router_B (config) # interface FastEthernet 0/0 Router_B (config) # ipv6 enable Router_B (config) # ipv6 address 2001:0:0:3:: 1/64 Router_B (config) # ipv6 rip 1 enable Now to define Tunnel Interface on Router_B Router_B (config) # interface Tunnel 0 Router_B (config) # ipv6 address 2001:0:0:5:: 2/64 Router_B (config) # tunnel source serial 1/0 Router_B (config) # tunnel destination Router_B (config) # tunnel mode ipv6ip Router_B (config) # ipv6 rip 1 enable Now to check the communication that whether the two router are communicating with each other using IPv4 cloud or not, we can check this by Ping or Traceroute Router_A# Ping ipv6 2001:0:0:3:: 1 OUTPUT: Types escape sequence to abort. Sending 5, 100-byte ICMP echos to 2001:0:0:3:: 1, timeout in 2 seconds:!!!!! Success rate is 100 percent <5/5>, round-trip min/avg/max = 12/58/188 ms Router_A# Traceroute OUTPUT: Types escape sequence to abort. Tracing the route to 2001:0:0:3:: :0:0:3:: 1 56 msec 48 msec 72 msec SUMMARY Some of the benefits of IPv6 seem obvious: greater addressing space, built-in QoS, and better routing performance and services. However, a number of barriers must be overcome before the implementation of IPv6. The biggest question for most of us will be what the business need is for moving from current IPv4 to IPv6. The killer app has not appeared yet, but it may be closer than we think. The second consideration is the cost it may not have much to do with hardware replacement cost. All the larger routers have up gradable OSs IOS; the only necessity is the commitment to upgrading IOS. More likely to do with training and support of minor IP devices such as printers and network faxes, they will support the new address space. IPv6 has schemes to support old and new, however, so this may not even be a barrier. The last issue to consider is training: This will need to happen sooner or later because we all need to start thinking about 128-bit addressing based on MAC addresses in HEX. This involves all new ways of addressing and will be an uncomfortable change for many people. This conclusion may seem negative, but the greater good will overpower all the up-front issues. The issue is not whether you will have to move to IPv6, but when! We all need IPv6; the increased address space is needed for the growth of IP appliances that we are starting to hear about weekly. IP-ready cars are already shipping today. This requires mobility, which is addressed in IPv6.Of course, a number of very important features have not been discussed in this section, including QoS, mobile IP, autoconfiguration, and security. All these areas are extremely important, and until IPv6 is finished, you should keep referring to the IETF Web site for the most current information. Several new books on IPv6 also are starting to show up on bookstore shelves and should provide the deeper technical detail on address headers and full packet details. One of the newest major standards on the horizon is IPv6.Although IPv6 has not officially become a standard, it is worth some overview. It is very possible that this information will change as we move closer to IPv6 as a standard, so you should use this as a guide into IPv6, not the definitive information. A number of books are now being published that cover in detail this emerging standard; if you are looking for more details you should refer to these books. All the RFCs available

11 International Journal of Video & Image Processing and Network Security IJVIPNS-IJENS Vol: 11 No: on the Internet have the raw details on how this standard is developing. However, these documents are difficult to interpret at first glance and require some commitment to going through any number of RFCs pertaining to many subjects all related to IPv6 development. Internet Protocol Version 4 is the most popular protocol in use today (see Chapter 31, Internet Protocols ), although there are some questions about its capability to serve the Internet community much longer. IPv4 was finished in the 1970s and has started to show its age. The main issue surrounding IPv6 is addressing or, the lack of addressing because many experts believe that we are nearly out of the four billion addresses available in IPv4. Although this seems like a very large number of addresses, multiple large blocks are given to government agencies and large organizations. IPv6 could be the solution to many problems, but it is still not fully developed and is not a standard yet! Many of the finest developers and engineering minds have been working on IPv6 since the early 1990s. Hundreds of RFCs have been written and have detailed some major areas, including expanded addressing, simplified header format, flow labeling, authentication, and privacy. Expanded addressing moves us from 32-bit address to a 128-bit addressing method. It also provides newer unicast and broadcasting methods, injects hexadecimal into the IP address, and moves from using. to using : as delimiters. REFERENCE [1] IPV6 The Next Generation Networking DEC-07-WW-ENG-LTR.PDF [2] IPV6 White Paper ALLIED TELESYN BO6162D9BF884EDA9BB527A470026ACE.PDF [3] Understanding IPV6 [4] IPV6 White Paper ALLIED TELESYN BO6162D9BF884EDA9BB527A470026ACE.PDF [5] European Journal of Specific Research ISSN X vol.34 No.1 (2009) pp [6] S.Hagen IPV6 Essentials, O Reilly July 2002 [7] K. Wang, A.K. Yeo and A.L. Ananda, DTTS: a Transparent and Scalable Solution for IPv4 to IPv6 Transition, Proceedings of the tenth International Conference on Computer Communications and Networks, 2001, pp [8] R. Gilligan, Transition Mechanisms for IPv6 Hosts and Routers, RFC2893, August 2000 [9] L. Zhou, V. Renesse and M. Marsh, Implementing IPv6 as a Peer-to-Peer Overlay Network, Proceedings of the 21st IEEE Symposium on Reliable Distributed Systems, 2002, pp [10] B. Carpenter and C. Jung, Transmission of IPv6 over IPv4 Domains without Explicit Tunnels, RFC2529, March 1999 [11] C. Huitema, An Anycast Prefix for 6to4 Relay Routers, RFC3068, June [12] Durand, P. Fasano, I. Guardini and D. Lento, IPv6 Tunnel Broker, RFC3053, January 2001 [13] E. Nordmark, Stateless IP/ICMP Translation Algorithm (SIIT), RFC2765, February 2000 [14] K. Tsuchiya, H. Higuchi and Y. Atarashi, Dual Stack Hosts using the "Bump-Inthe-Stack" Technique (BIS), RFC2767, February 2000 [15] G. Tsirtsis and P. Srisuresh, Network Address Translation- Protocol Translation (NAT-PT), RFC2766, February 2000 [16] G.C. Lee, M.K. Shin, H.J. Kim, Implementing NAT-PT/SIIT, ALGs and Consideration to the Mobility Support in NAT-PT environment, Proceedings of the 6th International Conference on Advanced Communication Technology, 2004, pp