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  • 1. Assignment IPV6 for IP Telephony Prepared for Dr. Mashiur Rahman Assistant Professor Department of Computer Science and Engineering North South University Name: Moushumi Maria ID# 071464056 ETE 605 Date: 15-04-2008 1
  • 2. Contents 1. Introduction .............................................................................................................................3 2. Background.............................................................................................................................3 3. Core protocols of IPv6 .............................................................................................................3 3.1 Internet Protocol version 6 (IPv6).......................................................................................3 3.2 Internet Control Message Protocol for IPv6 (ICMPv6) ........................................................4 3.3 Multicast Listener Discovery (MLD)....................................................................................5 3.4 Neighbor Discovery (ND)...................................................................................................6 4. IPv6 addressing and routing ....................................................................................................7 4.1 IPv6 address auto configuration.........................................................................................7 4.1.1 Auto configured address states ..................................................................................8 4.1.2 Types of auto configuration ........................................................................................8 4.1.3 Auto configuration process .........................................................................................9 4.2 IPv6 routing.......................................................................................................................9 4.2.1 IPv6 routers..............................................................................................................10 4.2.2 Routing tables ..........................................................................................................10 4.3 IPv6 addressing ..............................................................................................................11 4.3.1 IPv6 address space..................................................................................................11 4.3.2 Expressing IPv6 addresses ......................................................................................11 4.3.3 Unicast IPv6 addresses............................................................................................12 4.3.4 Multicast IPv6 addresses..........................................................................................13 4.3.5 Addresses for hosts and routers ...............................................................................13 5. Benefits of IPv6 if used in IP Telephony.................................................................................14 5.1 IP Telephony...................................................................................................................14 5.2 IP Telephony implementation overview............................................................................14 5.3 Features of IPv6 valuable for IP Telephony......................................................................14 5.3.1 New header format...................................................................................................15 5.3.2 Large address space ................................................................................................15 5.3.3 Efficient and hierarchical addressing and routing infrastructure.................................15 5.3.4 Stateless and stateful address configuration.............................................................15 5.3.5 Built-in security.........................................................................................................16 5.3.6 Better support for quality of service (QoS) ................................................................16 5.3.7 New protocol for neighboring node interaction ..........................................................16 5.3.8 Extensibility..............................................................................................................16 2
  • 3. 1. Introduction Internet Protocol version 6 (IPv6) is a network layer for packet-switched inter-networks. It is designated as the successor of IPv4, the current version of the Internet Protocol, for general use on the Internet. The main change brought by IPv6 is a much larger address space that allows greater flexibility in assigning addresses. The extended address length eliminates the need to use network address translation to avoid address exhaustion, and also simplifies aspects of address assignment and renumbering when changing providers. It was not the intention of IPv6 designers, however, to give permanent unique addresses to every individual and every computer. 2. Background By the early 1990s, it was clear that the change to a classless network introduced a decade earlier was not enough to prevent IPv4 address exhaustion and that further changes to IPv4 were needed. By the beginning of 1992, several proposed systems were being circulated and by the end of 1992, the IETF announced a call for white papers (RFC 1650) and the creation of the "IP, the Next Generation" (IPng Area) of working groups. IPng was adopted by the Internet Engineering Task Force on July 25, 1994 with the formation of several "IP Next Generation" (IPng) working groups. By 1996, a series of RFCs were released defining IPv6, starting with RFC 2460. (Incidentally, IPv5 was not a successor to IPv4, but an experimental flow-oriented streaming protocol intended to support video and audio.) 3. Core protocols of IPv6 3.1 Internet Protocol version 6 (IPv6) IPv6 is defined in RFC 2460, "Internet Protocol Version 6 (IPv6) Specification." IPv6 is a connectionless, unreliable datagram protocol used primarily for addressing and routing packets between hosts. Connectionless means that a session is not established before exchanging data. Unreliable means that delivery is not guaranteed. IPv6 always makes a best-effort attempt to deliver a packet. An IPv6 packet might be lost, delivered out of sequence, duplicated, or delayed. IPv6 does not attempt to recover from these types of errors. The acknowledgment of packets delivered and the recovery of lost packets are done by a higher-layer protocol, such as TCP. An IPv6 packet, also known as an IPv6 datagram, consists of an IPv6 header and an IPv6 payload, as shown in the following illustration. Figure 1: IPv6 packet 3
  • 4. The IPv6 header contains the following fields for addressing and routing. IPv6 header field Function Source Address The IPv6 address of the original source of the IPv6 packet. Destination The IPv6 address of the intermediate or final destination of the IPv6 packet. Address Hop Limit The number of network segments on which the packet is allowed to travel before being discarded by a router. 3.2 Internet Control Message Protocol for IPv6 (ICMPv6) Internet Control Message Protocol for IPv6 (ICMPv6) is a required IPv6 standard defined in RFC 2463, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification." With ICMPv6, hosts and routers that use IPv6 communication can report errors and send simple echo messages. The ICMPv6 protocol also provides a framework for the following: Multicast Listener Discovery (MLD) MLD is a series of three ICMPv6 messages that replace version 2 of the Internet Group Management Protocol (IGMP) for IPv4 to manage subnet multicast membership. Neighbor Discovery (ND) Neighbor Discovery is a series of five ICMPv6 messages that manage node-to-node communication on a link. Neighbor Discovery replaces Address Resolution Protocol (ARP), ICMPv4 Router Discovery, and the ICMPv4 Redirect message and provides additional functions. ICMPv6 messages are usually sent automatically when an IPv6 packet cannot reach its destination. ICMPv6 messages are encapsulated and sent as the payload of IPv6 packets, as shown in the following illustration. Figure 2: ICMPv6 message Different types of ICMPv6 messages are identified in the ICMPv6 header. Because ICMPv6 messages are carried in IPv6 packets, they are unreliable. 4
  • 5. 3.3 Multicast Listener Discovery (MLD) The use of multicasting in IP networks is defined as a TCP/IP standard in RFC 1112, "Internet Group Management Protocol (IGMP)." This RFC defines address and host extensions for the way in which IP hosts support multicasting. The same concepts originally developed for the current version of IP, known as IP version 4 (IPv4), also apply to IPv6. Multicast traffic is sent to a single address but is processed by multiple hosts. Multicasting is similar to a newsletter subscription. As only subscribers receive the newsletter when it is published, only host computers that belong to the multicast group receive and process traffic sent to the group's reserved address. The set of hosts listening on a specific multicast address is called a multicast group. Other important aspects of multicasting include the following: • Group membership is dynamic, allowing hosts to join and leave the group at any time. • The joining of multicast groups is performed through the sending of group membership messages. In IPv6, Multicast Listener Discovery (MLD) messages are used to determine group membership on a network segment, also known as a link or subnet. • Groups are not limited by size and members can be spread out across multiple network segments (if connecting routers support the forwarding of multicast traffic and group membership information). • A host can send traffic to the group's address without belonging to the corresponding group. IPv6 multicast addressing IPv6 multicast addresses are reserved and assigned from the Format Prefix 1111 1111 (0xFF). The following table is a partial list of IPv6 multicast addresses that are reserved for IPv6 multicasting and registered with the Internet Assigned Numbers Authority (IANA). IPv6 multicast Description address FF02::1 The all-nodes address used to reach all nodes on the same link. FF02::2 The all-routers address used to reach all routers on the same link. FF02::4 The all-Distance Vector Multicast Routing Protocol (DVMRP) routers address used to reach all DVMRP multicast routers on the same link. FF02::5 The all-Open Shortest Path First (OSPF) routers address used to reach all OSPF routers on the same link. FF02::6 The all-OSPF designated routers address used to reach all OSPF designated routers on the same link. FF02::1:FFXX:XXXX The solicited-node address used in the address resolution process to resolve the IPv6 address of a link-local node to its link-layer address. The last 24 bits (XX:XXXX) of the solicited-node address are the last 24 bits of an IPv6 unicast address. 5
  • 6. A single IPv6 multicast address identifies each multicast group. Each group's reserved IPv6 address is shared by all host members of the group who listen and receive any IPv6 messages sent to the group's address. IPv6 multicast addresses are mapped to a reserved set of media access control (MAC) multicast addresses. MLD messages MLD is used to exchange membership status information between IPv6 routers that support multicasting and members of multicast groups on a network segment. Host membership in a multicast group is reported by individual member hosts, and membership status is periodically polled by multicast routers. MLD is defined in RFC 2710, "Multicast Listener Discovery (MLD) for IPv6." MLD message types are described in the following table. MLD message Description type Multicast Sent by a multicast router to poll a network segment for group members. Queries can be Listener Query general (requesting group membership for all groups), or specific (requesting group membership for a specific group). Multicast Sent by a host when it joins a multicast group, or in response to an MLD Multicast Listener Listener Report Query sent by a router. Multicast Sent by a host when it leaves a host group and might be the last member of that group on Listener Done the network segment. MLD messages are sent as ICMPv6 messages. 3.4 Neighbor Discovery (ND) IPv6 Neighbor Discovery (ND) is a set of messages and processes that determine relationships between neighboring nodes. ND replaces Address Resolution Protocol (ARP), Internet Control Message Protocol (ICMP) Router Discovery, and ICMP Redirect, which are used in IPv4, and provides additional functionality. ND is described in RFC 2461, "Neighbor Discovery for IP Version 6 (IPv6)." ND is used by hosts to: • Discover neighboring routers. • Discover addresses, address prefixes, and other configuration parameters. ND is used by routers to: • Advertise their presence, host configuration parameters, and on-link prefixes. • Inform hosts of a better next-hop address to forward packets for a specific destination. ND is used by nodes to: • Both resolve the link-layer address of a neighboring node to which an IPv6 packet is being forwarded and determine when the link-layer address of a neighboring node has changed. 6
  • 7. • Determine whether IPv6 packets can be sent to and received from a neighbor. The following table lists and describes ND processes. Process Description Router discovery The process by which a host discovers the local routers on an attached link (equivalent to ICMPv4 Router Discovery) and automatically configures a default router (equivalent to a default gateway in IPv4). Prefix discovery The process by which a host discovers the network prefixes for local destinations. Parameter The process by which a host discovers additional operating parameters, including the discovery link maximum transmission unit (MTU) and the default hop limit for outbound packets. Address auto The process for configuring IP addresses for interfaces in either the presence or configuration absence of a stateful address configuration server such as Dynamic Host Configuration Protocol version 6 (DHCPv6). Address resolution The process by which a node resolves a neighboring node's IPv6 address to its link- layer address (equivalent to ARP in IPv4). The resolved link-layer address becomes an entry in a node's neighbor cache (equivalent to the ARP cache in IPv4. Next-hop The process by which a node determines the IPv6 address of the neighbor to which a determination packet is being forwarded based on the destination address. Neighbor The process by which a node determines that IPv6 packets cannot be sent to and unreachability received from a neighboring node. detection Duplicate address The process by which a node determines that an address considered for use is not detection already in use by a neighboring node (equivalent to the use of gratuitous ARP frames in IPv4). Redirect function The process by which a router informs a host of a better first-hop IPv6 address to reach a destination (equivalent to the function of the IPv4 ICMP Redirect message). 4. IPv6 addressing and routing This section covers: 1. IPv6 address auto configuration 2. IPv6 routing 3. IPv6 Addressing 4.1 IPv6 address auto configuration A highly useful aspect of IPv6 is its ability to automatically configure itself without the use of a stateful configuration protocol, such as Dynamic Host Configuration Protocol for IPv6 (DHCPv6). 7
  • 8. By default, an IPv6 host can configure a link-local address for each interface. By using router discovery, a host can also determine the addresses of routers, additional addresses, and other configuration parameters. Included in the Router Advertisement message is an indication of whether a stateful address configuration protocol should be used. Address auto configuration can only be performed on multicast-capable interfaces. Address auto configuration is described in RFC 2462, "IPv6 Stateless Address Auto configuration." 4.1.1 Auto configured address states Auto configured addresses are in one or more of the following states: 1. Tentative 2. Preferred 3. Deprecated 4. Valid 5. Invalid The relationship between the states of an auto configured address and the preferred and valid lifetimes are shown in the following illustration. Figure 3: Auto configuration address states With the exception of link-local addresses, address auto configuration is only specified for hosts. Routers must obtain address and configuration parameters through another means (for example, manual configuration). 4.1.2 Types of auto configuration There are three types of auto configuration: 1. Stateless Configuration of addresses is based on the receipt of Router Advertisement messages. These messages include stateless address prefixes and require that hosts not use a stateful address configuration protocol. 2. Stateful Configuration is based on the use of a stateful address configuration protocol, such as DHCPv6, to obtain addresses and other configuration options. A host uses stateful address configuration when it receives Router Advertisement messages that do not include address prefixes and require that the host use a stateful address configuration protocol. A host will also use a stateful address configuration protocol when there are no routers present on the local link. 3. Both 8
  • 9. Configuration is based on receipt of Router Advertisement messages. These messages include stateless address prefixes and require that hosts use a stateful address configuration protocol. For all auto configuration types, a link-local address is always configured. 4.1.3 Auto configuration process The address auto configuration process for an IPv6 node occurs as follows: 1. A tentative link-local address is derived, based on the link-local prefix of FE80::/64 and the 64-bit interface identifier. 2. Duplicate address detection is performed to verify the uniqueness of the tentative link- local address. 3. If duplicate address detection fails, manual configuration must be performed on the node. 4. If duplicate address detection succeeds, the tentative link-local address is assumed to be unique and valid. The link-local address is initialized for the interface. The corresponding solicited-node multicast link-layer address is registered with the network adapter. For an IPv6 host, address auto configuration continues as follows: 1. The host sends a Router Solicitation message. 2. If no Router Advertisement messages are received, then the host uses a stateful address configuration protocol to obtain addresses and other configuration parameters. 3. If a Router Advertisement message is received, the configuration information that is included in the message is set on the host. 4. For each stateless auto configuration address prefix that is included: a. The address prefix and the appropriate 64-bit interface identifier are used to derive a tentative address. b. Duplicate address detection is used to verify the uniqueness of the tentative address. If the tentative address is in use, the address is not initialized for the interface. If the tentative address is not in use, the address is initialized. This includes setting the valid and preferred lifetimes based on information included in the Router Advertisement message. If it is specified in the Router Advertisement message, the host uses a stateful address configuration protocol to obtain additional addresses or configuration parameters. 4.2 IPv6 routing Routing is the process of forwarding packets between connected network segments. For IPv6- based networks, routing is the part of IPv6 that provides forwarding capabilities between hosts that are located on separate segments within a larger IPv6-based network. IPv6 is the mailroom in which IPv6 data sorting and delivery occur. Each incoming or outgoing packet is called an IPv6 packet. An IPv6 packet contains both the source address of the sending host and the destination address of the receiving host. Unlike link-layer addresses, IPv6 addresses in the IPv6 header typically remain the same as the packet travels across an IPv6 network. Routing is the primary function of IPv6. IPv6 packets are exchanged and processed on each host by using IPv6 at the Internet layer. Above the IPv6 layer, transport services on the source host pass data in the form of TCP segments or UDP messages down to the IPv6 layer. The IPv6 layer creates IPv6 packets with 9
  • 10. source and destination address information that is used to route the data through the network. The IPv6 layer then passes packets down to the link layer, where IPv6 packets are converted into frames for transmission over network-specific media on a physical network. This process occurs in reverse order on the destination host. IPv6 layer services on each sending host examine the destination address of each packet, compare this address to a locally maintained routing table, and then determine what additional forwarding is required. IPv6 routers are attached to two or more IPv6 network segments that are enabled to forward packets between them. 4.2.1 IPv6 routers IPv6 network segments, also known as links or subnets, are connected by IPv6 routers, which are devices that pass IPv6 packets from one network segment to another. This process is known as IPv6 routing and is shown in the following illustration. Figure 4: IPv6 routing IPv6 routers provide the primary means for joining together two or more physically separated IPv6 network segments. All IPv6 routers have the following characteristics: • IPv6 routers are physically multihomed hosts. A physically multihomed host is a network host that uses two or more network connection interfaces to connect to each physically separated network segment. • IPv6 routers provide packet forwarding for other IPv6 hosts. IPv6 routers are distinct from other hosts that use multihoming. An IPv6 router must be able to forward IPv6-based communication between networks for other IPv6 network hosts. You can implement IPv6 routers by using a variety of hardware and software products, including a computer running a member of the Windows Server 2003 family with the IPv6 protocol. Routers that are dedicated hardware devices running specialized software are common. Regardless of the type of IPv6 routers that you use, all IPv6 routing relies on a routing table to communicate between network segments. 4.2.2 Routing tables IPv6 hosts use a routing table to maintain information about other IPv6 networks and IPv6 hosts. Network segments are identified by using an IPv6 network prefix and prefix length. In addition, routing tables provide important information for each local host regarding how to communicate with remote networks and hosts. 10
  • 11. For each computer on an IPv6 network, you can maintain a routing table with an entry for every other computer or network that communicates with that local computer. In general, this is not practical, and a default router is used instead. Before a computer sends an IPv6 packet, it inserts its source IPv6 address and the destination IPv6 address (for the recipient) into the IPv6 header. The computer then examines the destination IPv6 address, compares it to a locally maintained IPv6 routing table, and takes appropriate action. The computer does one of three things: • It passes the packet to a protocol layer above IPv6 on the local host. • It forwards the packet through one of its attached network interfaces. • It discards the packet. IPv6 searches the routing table for the route that is the closest match to the destination IPv6 address. The most specific to the least specific route is determined in the following order: 1. A route that matches the destination IPv6 address (a host route with a 128-bit prefix length). 2. A route that matches the destination with the longest prefix length. 3. The default route (the network prefix ::/0). If a matching route is not found, the destination is determined to be an on-link destination. 4.3 IPv6 addressing This section covers: 1. IPv6 address space 2. Expressing IPv6 addresses 3. Unicast IPv6 addresses 4. Multicast IPv6 addresses 5. Addresses for hosts and routers 4.3.1 IPv6 address space The most obvious distinguishing feature of IPv6 is its use of much larger addresses. The size of an address in IPv6 is 128 bits, which is four times larger than an address in IPv4. A 32-bit address space allows for 232 or 4,294,967,296 possible addresses. A 128-bit address space allows for 2128 or 340,282,366,920,938,463,463,374,607,431,768,211,456 (3.4 × 1038) possible addresses. In the late 1970s when the IPv4 address space was designed, it was unimaginable that it could be exhausted. However, due to changes in technology and an allocation practice that did not anticipate the recent explosion of hosts on the Internet, the IPv4 address space was consumed to the point that by 1992, it was clear a replacement would be necessary. 4.3.2 Expressing IPv6 addresses IPv4 addresses are represented in dotted-decimal format. This 32-bit address is divided along 8- bit boundaries. Each set of 8 bits is converted to its decimal equivalent and separated by periods. For IPv6, the 128-bit address is divided along 16-bit boundaries, and each 16-bit block is converted to a 4-digit hexadecimal number and separated by colons. The resulting representation is called colon-hexadecimal. 11
  • 12. The following is an IPv6 address in binary form: 0010000111011010000000001101001100000000000000000010111100111011 0000001010101010000000001111111111111110001010001001110001011010 The 128-bit address is divided along 16-bit boundaries, as follows: 0010000111011010 0000000011010011 0000000000000000 0010111100111011 0000001010101010 0000000011111111 1111111000101000 1001110001011010 Each 16-bit block is converted to hexadecimal and delimited with colons. The result is: 21DA:00D3:0000:2F3B:02AA:00FF:FE28:9C5A IPv6 representation can be further simplified by removing the leading zeros within each 16-bit block. However, each block must have at least a single digit. With leading zero suppression, the address representation becomes: 21DA:D3:0:2F3B:2AA:FF:FE28:9C5A 4.3.3 Unicast IPv6 addresses A unicast address identifies a single interface within the scope of the type of unicast address. With the appropriate unicast routing topology, packets addressed to a unicast address are delivered to a single interface. The following types of addresses are unicast IPv6 addresses: • Aggregatable global unicast addresses • Link-local addresses • Site-local addresses • Special addresses • Compatibility addresses • NSAP addresses Figure 5: Unicast address bits The following illustration shows how the fields within the aggregatable global unicast address create a three-level topological structure. Figure 6: Unicast address topological structure 12
  • 13. 4.3.4 Multicast IPv6 addresses A multicast address identifies multiple interfaces. With the appropriate multicast routing topology, packets addressed to a multicast address are delivered to all interfaces that are identified by the address. IPv6 multicast addresses have the Format Prefix (FP) of 1111 1111. An IPv6 address is simple to classify as multicast because it always begins with FF. Multicast addresses cannot be used as source addresses. Beyond the FP, multicast addresses include additional structure to identify their flags, scope, and multicast group, as shown in the following illustration. Figure 7: Multicast address 4.3.5 Addresses for hosts and routers An IPv4 host with a single network adapter typically has a single IPv4 address assigned to that adapter. An IPv6 host, however, usually has multiple IPv6 addresses, even with a single interface. An IPv6 host is assigned the following unicast addresses: 1. A link-local address for each interface. 2. Unicast addresses for each interface (which could be a site-local address and one or multiple global addresses). 3. The loop back address (::1) for the loop back interface. Typical IPv6 hosts are logically multihomed because they have at least two addresses with which they can receive packets. Each host has a link-local address for local link traffic and a routable site-local or global address. Additionally, each host is listening for traffic on the following multicast addresses: 1. The node-local scope all-nodes address (FF01::1). 2. The link-local scope all-nodes address (FF02::1). 3. The solicited-node address for each unicast address on each interface. 4. The multicast addresses of joined groups on each interface. An IPv6 router is assigned the following unicast addresses: A link-local address for each interface 1. Unicast addresses for each interface (which might be a site-local address and one or multiple aggregatable global unicast addresses). 2. The loop back address (::1) for the loop back interface. An IPv6 router is assigned the following any cast addresses: 1. A subnet-router any cast address for each subnet. 13
  • 14. 2. Additional any cast addresses (optional). Additionally, each router is listening for traffic on the following multicast addresses: 1. The node-local scope all-nodes address (FF01::1) 2. The node-local scope all-routers address (FF01::2) 3. The link-local scope all-nodes address (FF02::1) 4. The link-local scope all-routers address (FF02::2) 5. The site-local scope all-routers address (FF05::2) 6. The solicited-node address for each unicast address on each interface 7. The addresses of joined groups on each interface 5. Benefits of IPv6 if used in IP Telephony 5.1 IP Telephony IP telephony is a term used to describe a suite of products and solutions used to transport voice traffic over a data network. Utilizing Internet Protocol (IP) as a transport mechanism, IP telephony allows you to create a converged network in which all communications (voice, video, or data) share the same infrastructure. 5.2 IP Telephony implementation overview Voice traffic and regular IP data traffic are two completely different solutions. Regular Transmission Control Protocol/IP (TCP/IP) data traffic is very resilient. It can be forgiving of slow wide area network (WAN) links, lost packets, and the reception of packets out of sequence. In fact, TCP/IP operates in just that way, taking data and segmenting it into several packets and transmitting the data via the best possible path. It is not concerned with the order in which the data is received, or the path it takes to get there, because the end device is responsible for the reassembly and re-segmentation of the data. Voice traffic, on the other hand, is not so forgiving, nor as resilient. Even though the voice traffic is being converted to IP packets, it is still voice traffic. IP telephony depends on packets being received in the same order in which they were sent; if a packet is lost, then it should remain lost, as retransmitting the packet would only confuse the person on the receiving end of the call. In order to accomplish this, you must incorporate several new features on your routers and switches, such as Queuing and Real-Time Transport Protocol (RTP). In fact, in order to make IP telephony a reality, the infrastructure is going to need quite a few enhancements. There are several components that must be added to the infrastructure. These components include, but are not limited to, specialized router interfaces, specialized local area network (LAN) switch modules and interfaces, IP telephone handsets, Call Manager servers as well as other unified messaging solutions. In addition to the required hardware, there are several applications that will also help you to realize the benefits of IP telephony. 5.3 Features of IPv6 valuable for IP Telephony The following are the features of the IPv6 considered to be valuable for IP Telephony domain: 1. New header format 2. Large address space 3. Efficient and hierarchical addressing and routing infrastructure 4. Stateless and stateful address configuration 14
  • 15. 5. Built-in security 6. Better support for quality of service (QoS) 7. New protocol for neighboring node interaction 8. Extensibility The following sections discuss each of these new features in brief. 5.3.1 New header format The IPv6 header has a new format that is designed to minimize header overhead. This is achieved by moving both nonessential fields and option fields to extension headers that are placed after the IPv6 header. The streamlined IPv6 header provides more efficient processing at intermediate routers. IPv4 headers and IPv6 headers are not interoperable and the IPv6 protocol is not backward compatible with the IPv4 protocol. A host or router must use an implementation of both IPv4 and IPv6 in order to recognize and process both header formats. The new IPv6 header is only twice as large as the IPv4 header, even though IPv6 addresses are four times as large as IPv4 addresses. 5.3.2 Large address space IPv6 has 128-bit (16-byte) source and destination addresses. Although 128 bits can provide over 3.4×1038 possible combinations, the large address space of IPv6 has been designed to allow for multiple levels of subnetting and address allocation from the Internet backbone to the individual subnets within an organization. Although only a small percentage of possible addresses are currently allocated for use by hosts, there are plenty of addresses available for future use. With a much larger number of available addresses, address-conservation techniques, such as the deployment of NATs, are no longer necessary. 5.3.3 Efficient and hierarchical addressing and routing infrastructure IPv6 global addresses used on the IPv6 portion of the Internet are designed to create an efficient, hierarchical, and summarized routing infrastructure that addresses the common occurrence of multiple levels of Internet service providers. On the IPv6 Internet, backbone routers have much smaller routing tables. 5.3.4 Stateless and stateful address configuration To simplify host configuration, IPv6 supports both stateful address configuration, such as address configuration in the presence of a DHCP server, and stateless address configuration (address configuration in the absence of a DHCP server). With stateless address configuration, hosts on a link automatically configure themselves with IPv6 addresses for the link (link-local addresses) and with addresses that are derived from prefixes advertised by local routers. Even in the absence of a router, hosts on the same link can automatically configure themselves with link-local addresses and communicate without manual configuration. 15
  • 16. 5.3.5 Built-in security Support for IPSec is an IPv6 protocol suite requirement. This requirement provides a standards- based solution for network security needs and promotes interoperability between different IPv6 implementations. 5.3.6 Better support for quality of service (QoS) New fields in the IPv6 header define how traffic is handled and identified. Traffic identification, by using a Flow Label field in the IPv6 header, allows routers to identify and provide special handling for packets that belong to a flow. A flow is a series of packets between a source and destination. Because the traffic is identified in the IPv6 header, support for QoS can be easily achieved even when the packet payload is encrypted with IPSec. 5.3.7 New protocol for neighboring node interaction The Neighbor Discovery protocol for IPv6 is a series of Internet Control Message Protocol for IPv6 (ICMPv6) messages that manage the interaction of neighboring nodes (that is, nodes on the same link). Neighbor Discovery replaces Address Resolution Protocol (ARP), ICMPv4 Router Discovery, and ICMPv4 Redirect messages with efficient multicast and unicast messages and provides additional functionality. 5.3.8 Extensibility IPv6 can be extended for new features by adding extension headers after the IPv6 header. Unlike the IPv4 header, which can only support 40 bytes of options, the size of IPv6 extension headers is only constrained by the size of the IPv6 packet. 16