ch2.pdf

JTO Ph-II DNIT Overview of IPv6 2 OVERVIEW OF IPV6 2.1 LEARNING OBJECTIVES The objectives of this chapter is to understand i) Importance Of IPv6 ii) IPv6 Address Represen...

JTO Ph-II DNIT Overview of IPv6 2 OVERVIEW OF IPV6 2.1 LEARNING OBJECTIVES The objectives of this chapter is to understand i) Importance Of IPv6 ii) IPv6 Address Representation iii) Parts Of IPv6 Address & Address Allocation Concept iv) IPv6 Protocols & Advantages v) Types And Scope Of IPv6 Address vi) Address Assignment Features Of IPv6 2.2 IPV6 INTRODUCTION IPv4 has been a solid and highly useful part of the growth of TCP/IP and the Internet. For most of the long history of the Internet, and for most corporate networks that use TCP/IP, IPv4 is the core protocol that defines addressing and routing. However, even though IPv4 has many great qualities, it does have some shortcomings, creating the need for a replacement protocol: IP version 6 (IPv6). IPv6 defines the same general functions as IPv4, but with different methods of implementing those functions. For example, both IPv4 and IPv6 define addressing, the concepts of subnetting larger groups of addresses into smaller groups, headers used to create an IPv4 or IPv6 packet, and the rules for routing those packets. At the same time, IPv6 handles the details differently; for example, using a 128-bit IPv6 address rather than the 32-bit IPv4 address. 2.3 WHY IS IPV6 IMPORTANT? IPv6 is the latest version of the Internet Protocol, which identifies devices across the internet so they can be located. Every device that uses the internet is identified through its own IP address in order for internet communication to work. In that respect, it‘s just like the street addresses and zip codes you need to know in order to mail a letter. The previous version, IPv4, uses a 32-bit addressing scheme to support 4.3 billion devices, which was thought to be enough. However, the growth of the internet, personal computers, smart phones and now Internet of Things devices proves that the world needed more addresses. Fortunately, the Internet Engineering Task Force (IETF) recognized this 20 years ago. In 1998 it created IPv6, which instead uses 128-bit addressing to support approximately 340 trillion trillion (or 2 to the 128th power, if you like). Instead of the IPv4 address method of four sets of one- to three-digit numbers, IPv6 uses eight groups of four hexadecimal digits, separated by colons. JTO Ph –II Version 3.0 Aug 2021 Page 18 of 136 For Restricted Circulation JTO Ph-II DNIT Overview of IPv6 2.4 FEATURES OF IPV6 To a great extent, IPv6 is a conservative extension of IPv4. Most transport- and application-layer protocols need little or no change to work over IPv6; exceptions are applications protocols that embed network-layer addresses (such as FTP or NTPv3). Applications, however, usually need small changes and a recompile in order to run over IPv6. 2.4.1 LARGER ADDRESS SPACE The main feature of IPv6 that is driving adoption today is the larger address space: addresses in IPv6 are 128 bits long versus 32 bits in IPv4. The larger address space avoids the potential exhaustion of the IPv4 address space without the need for NAT and other devices that break the end-to-end nature of Internet traffic. It also makes administration of medium and large networks simpler, by avoiding the need for complex Subnetting schemes. The drawback of the large address size is that IPv6 carries some bandwidth overhead over IPv4, which may hurt regions where bandwidth is limited (header compression can sometimes be used to alleviate this problem). 2.4.2 STATELESS AUTOCONFIGURATION OF HOSTS IPv6 hosts can be configured automatically when connected to a routed IPv6 network. When first connected to a network, a host sends a link-local multicast (broadcast) request for its configuration parameters; if configured suitably, routers respond to such a request with a router advertisement packet that contains network-layer configuration parameters. If IPv6 auto-configuration is not suitable, a host can use stateful auto- configuration (DHCPv6) or be configured manually. Stateless auto-configuration is only suitable for hosts: routers must be configured manually or by other means. 2.4.3 MULTICAST Multicast is part of the base protocol suite in IPv6. This is in opposition to IPv4, where multicast is optional. Most environments do not currently have their network infrastructures configured to route multicast; that is the link-scoped aspect of multicast will work but the site-scope, organization-scope and global-scope multicast will not be routed. 2.4.4 JUMBOGRAMS In IPv4, packets are limited to 64 KB of payload. When used between capable communication partners and on communication links with a MTU larger than 65,576 octets, IPv6 has optional support for packets over this limit, referred to as jumbograms which can be as large as 4 GB. The use of jumbograms may improve performance over high-MTU networks. JTO Ph –II Version 3.0 Aug 2021 Page 19 of 136 For Restricted Circulation JTO Ph-II DNIT Overview of IPv6 2.4.5 NETWORK-LAYER SECURITY IPsec, the protocol for IP network-layer encryption and authentication, is an integral part of the base protocol suite in IPv6; this is unlike IPv4, where it is optional (but usually implemented). IPsec, however, is not widely deployed except for securing traffic between IPv6 BGP routers. 2.4.6 MOBILITY Unlike mobile IPv4, Mobile IPv6 (MIPv6) avoids triangular routing and is therefore as efficient as normal IPv6. This advantage is mostly hypothetical, as neither MIP nor MIPv6 are widely deployed today. 2.4.7 ADDRESSING 128-bit length The primary change from IPv4 to IPv6 is the length of network addresses. IPv6 addresses are 128 bits long (as defined by RFC 4291), whereas IPv4 addresses are 32 bits; where the IPv4 address space contains roughly 4 billion addresses, IPv6 has enough room for 3.4×1038 unique addresses. IPv6 addresses are typically composed of two logical parts: a 64-bit (sub-)network prefix, and a 64-bit host part, which is either automatically generated from the interface's MAC address or assigned sequentially. Because the globally unique MAC addresses offer an opportunity to track user equipment, and so users, across time and IPv6 address changes, 2.5 IPV6 ADDRESS REPRESENTATION 64 bit Network prefix 64 bit Interface ID H H H H H H H H HHH HHH HHH HHH HHH HHH HHH HHH 128 bits HHHH = Hex value 0000 to FFFF Figure 9: IPv6 Address Format An IPv6 address is represented as (colon separated hexa decimal notation) eight groups of four hexadecimal digits, each group representing 16 bits (two octets, a group sometimes also called a hextet). The groups are separated by colons (:). An example of an IPv6 address is: 2001:0db8:85a3:0000:0000:8a2e:0370:7334 Notation IPv6 addresses are normally written as eight groups of four hexadecimal digits. JTO Ph –II Version 3.0 Aug 2021 Page 20 of 136 For Restricted Circulation JTO Ph-II DNIT Overview of IPv6 Example- 2001:0db8:85a3:08d3:1319:8a2e:0370:7334 is a valid IPv6 address. To reduce the complexity if a four-digit group is 0000, the zeros may be omitted and replaced with two colons(::). Example- 2001:0db8:0000:0000:0000:0000:1428:57ab can be shortened as 2001:0db8::1428:57ab. Following this rule, any number of consecutive 0000 groups may be reduced to two colons, as long as there is only one double colon used in an address. Leading zeros in a group can also be omitted. Thus, the addresses below are all valid and equivalent: 2001:0db8:0000:0000:0000:0000:1428:57ab 2001:0db8:0000:0000:0000::1428:57ab 2001:0db8:0:0:0:0:1428:57ab 2001:0db8:0:0::1428:57ab 2001:0db8::1428:57ab 2001:db8::1428:57ab Having more than one double-colon abbreviation in an address is invalid, as it would make the notation ambiguous. A sequence of 4 bytes at the end of an IPv6 address can also be written in decimal, using dots as separators. This notation is often used with compatibility addresses (see below). Thus, ::ffff:1.2.3.4 is the same address as ::ffff:0102:0304, and ::ffff:15.16.18.31 is the same address as ::ffff:0f10:121f. Literal IPv6 Addresses in URLs In a URL the IPv6-Address is enclosed in brackets. Example: http://[2001:0db8:85a3:08d3:1319:8a2e:0370:7344]/ This notation allows parsing a URL without confusing the IPv6 address and port number: http://[2001:0db8:85a3:08d3:1319:8a2e:0370:7344]:443/ Network notation IPv6 networks are written using CIDR notation. An IPv6 network (or subnet) is a contiguous group of IPv6 addresses the size of which must be a power of two; the initial bits of addresses, which are identical for all hosts in the network, are called the network's prefix. A network is denoted by the first address in the network and the size in bits of the prefix (in decimal), separated with a slash. Example- 2001:0db8:1234::/48 stands for the network with addresses JTO Ph –II Version 3.0 Aug 2021 Page 21 of 136 For Restricted Circulation JTO Ph-II DNIT Overview of IPv6 2001:0db8:1234:0000:0000:0000:0000:0000 through 2001:0db8:1234:FFFF:FFFF:FFFF:FFFF:FFFF Because a single host can be seen as a network with a 128-bit prefix, you will sometimes see host addresses written followed with /128. 2.5.1 GUIDELINES TO SHORTEN THE IPV6 ADDRESS REPRESENTATION: The standards provide flexibility in the representation of IPv6 addresses. The full representation of eight four-digit groups may be simplified by several techniques, eliminating parts of the representation. In general, representations are shortened as much as possible. IETF recommendations suggest the use of only lower case letters. For example, 2001:db8::1 is preferred over 2001:DB8::1. Leading zeros in each 16-bit field are suppressed, but each group must retain at least one digit in the case of the all-zero group. For example, 2001:0db8::0001:0000 is rendered as 2001:db8::1:0. The all-zero field that is explicitly presented is rendered as 0. The longest sequence of consecutive all-zero fields is replaced with two colons ("::"). If the address contains multiple runs of all-zero fields, then it is the leftmost that is compressed to prevent ambiguities. For example, 2001:db8:0:0:1:0:0:1 is rendered as 2001:db8::1:0:0:1 "::" is not used to represent just a single all-zero field. For example, 2001:db8:0:0:0:0:2:1 is shortened to 2001:db8::2:1, but 2001:db8:0000:1:1:1:1:1 is rendered as 2001:db8:0:1:1:1:1:1. These methods can lead to very short representations for IPv6 addresses. For example, the localhost (loopback) address, 0:0:0:0:0:0:0:1, and the IPv6 unspecified address, 0:0:0:0:0:0:0:0, are reduced to ::1 and ::, respectively. During the transition of the Internet from IPv4 to IPv6, it is typical to operate in a mixed addressing environment. For such use cases, a special notation has been introduced, which expresses IPv4-mapped and IPv4-compatible IPv6 addresses by writing the least-significant 32 bits of an address in the familiar IPv4 dot-decimal notation, whereas the 96 most-significant bits are written in IPv6 format. For example, the IPv4-mapped IPv6 address ::ffff:c000:0280 is written as ::ffff:192.0.2.128, thus expressing clearly the original IPv4 address that was mapped to IPv6. 2.5.2 PARTS OF IPV6 ADDRESS & ADDRESS ALLOCATION JTO Ph –II Version 3.0 Aug 2021 Page 22 of 136 For Restricted Circulation JTO Ph-II DNIT Overview of IPv6 Figure 10: IPv6 Address Components Only one eighth of the total address space is currently allocated for use on the Internet, 2000::/3, in order to provide efficient route aggregation, thereby reducing the size of the Internet routing tables; the rest of the IPv6 address space is reserved for future use or for special purposes. The address space is assigned to the RIRs in large blocks of /23 up to /12.The RIRs assign smaller blocks typically in sizes from /19 to /32 to local Internet registries that distribute them to users. These addresses are typically distributed in /48 sized blocks to the end users. Each RIR can divide each of its multiple /23 blocks into 512 /32 blocks, typically one for each ISP; an ISP can divide its /32 block into 65536 /48 blocks, typically one for each customer; customers can create 65536 /64 networks from their assigned /48 block, each having 264 (18,446,744,073,709,551,616) addresses. In contrast, the entire IPv4 address space has only 232 (exactly 4,294,967,296 or about 4.3×109) addresses. By design, only a very small fraction of the address space will actually be used. The large address space ensures that addresses are almost always available, which makes the use of network address translation (NAT) for the purposes of address conservation completely unnecessary. NAT has been increasingly used for IPv4 networks to help alleviate IPv4 address exhaustion. Figure 11: IPv6 Address Allocation – Prefix values 2.6 ADVANTAGES OF IPV6 a. More efficient address space allocation b. End to end addressing without NAT c. Fragmentation only at the source host d. Routers do not calculate header checksum e. No broadcast, uses multicast instead f. Built –in security mechanisms g. Auto-configuration of addresses h. Headers are modular/ extensible 2.7 IPV6 PROTOCOLS The primary purpose of the core IPv6 protocol mirrors the same purpose of the IPv4 protocol. That core IPv6 protocol, as defined in RFC 2460, defines a packet concept, addresses for those packets, and the role of hosts and routers. These rules allow the JTO Ph –II Version 3.0 Aug 2021 Page 23 of 136 For Restricted Circulation JTO Ph-II DNIT Overview of IPv6 devices to forward packets sourced by hosts, through multiple routers, so that they arrive at the correct destination host. IPv6 supports the following routing protocols:  RIPng (RIP New Generation)  OSPFv3  EIGRP for IPv6  IS-IS for IPv6  MP-BGP4 (Multiprotocol BGP-4) 2.7.1 ICMP UPGRADED TO ICMP VERSION 6 Internet Control Message Protocol (ICMP) worked well with IPv4 but needed to be changed to support IPv6. The new name is ICMPv6. 2.7.2 ARP REPLACED BY NEIGHBOR DISCOVERY PROTOCOL For IPv4, Address Resolution Protocol (ARP) discovers the MAC address used by neighbors. IPv6 replaces ARP with a more general Neighbor Discovery Protocol (NDP) 2.7.3 DYNAMIC HOST CONFIGURATION PROTOCOL VERSION 6 (DHCPV6) Network protocol for configuring Internet Protocol version 6 (IPv6) hosts with IP addresses, IP prefixes and other configuration data required to operate in an IPv6 network. It is the IPv6 equivalent of the Dynamic Host Configuration Protocol for IPv4. 2.8 COMPARE AND CONTRAST IPV6 ADDRESS TYPES IPv4 address is split by class, with Classes A, B, and C defining unicast IPv4 addresses. (The term unicast refers to the fact that each address is used by only one interface.) Then, within the Class A, B, and C address range, the Internet Assigned Numbers Authority (IANA) and the Internet Corporation for Assigned Names and Numbers (ICANN) reserve most of the addresses as public IPv4 addresses, with a few reserved as private IPv4 addresses. IPv6 does not use any concept like the classful network concept used by IPv4. 2.9 IPV6 ADDRESS TYPES IPv4 supports unicast, broadcast, and multicast addresses that basically define who or at least how many other devices we‘re talking to. IPv6 modifies that trio and introduces the anycast. Broadcasts, have been eliminated in IPv6 because of their cumbersome inefficiency. 2.9.1 GLOBAL UNICAST ADDRESSES (2000::/3) These are typical publicly routable addresses and they‘re the same as in IPv4. Global addresses start at 2000::/3. Figure 14.2 shows how a unicast address breaks down. The ISP can provide you with a minimum /48 network ID, which in turn provides you 16- bits to create a unique 64-bit router interface address. The last 64-bits are the unique host ID. JTO Ph –II Version 3.0 Aug 2021 Page 24 of 136 For Restricted Circulation JTO Ph-II DNIT Overview of IPv6 2.9.2 IPV6 GLOBAL ROUTING PREFIX IPv6 global unicast addresses allow IPv6 to work more like the original design of the IPv4 Internet. Each organization asks for a block of IPv6 addresses, which no one else can use. That organization further subdivides the address block into smaller chunks, called subnets. Finally, to choose what IPv6 address to use for any host, the engineer chooses an address from the right subnet. That reserved block of IPv6 addresses—a set of addresses that only one company can use— is called a global routing prefix. Each organization that wants to connect to the Internet and use IPv6 global unicast addresses should ask for and receive a global routing prefix. Very generally, you can think of the global routing prefix like an IPv4 Class A, B, or C network number from the range of public IPv4 addresses. The term global routing prefix might not make you think of a block of IPv6 addresses at first. The term actually refers to the idea that Internet routers can have one route that refers to all the addresses inside the address block, without a need to have routes for smaller parts of that block. Figure 12: IPv6 Global Routing Prefix 2.9.3 LINK-LOCAL ADDRESSES (FE80::/10) These are like the Automatic Private IP Address (APIPA) addresses that Microsoft uses to automatically provide addresses in IPv4 in that they‘re not meant to be routed. In IPv6 they start with FE80::/10, as shown in Figure 14.3. Think of these addresses as handy tools that give you the ability to throw a temporary LAN together for meetings or create a small LAN that‘s not going to be routed but still needs to share and access files and services locally. 2.9.4 UNIQUE LOCAL ADDRESSES (FC00::/7) These addresses are also intended for non-routing purposes over the Internet, but they are nearly globally unique, so it‘s unlikely you‘ll ever have one of them overlap. Unique local addresses were designed to replace site-local addresses, so they basically do almost exactly what IPv4 private addresses do: allow communication throughout a site while being routable to multiple local networks. Site-local addresses were deprecated as of September 2004. 2.9.5 MULTICAST (FF00::/8) As in IPv4, packets addressed to a multicast address are delivered to all interfaces tuned into the multicast address. Sometimes people call them ―one-to-many‖ addresses. It‘s really easy to spot a multicast address in IPv6 because they always start with FF. JTO Ph –II Version 3.0 Aug 2021 Page 25 of 136 For Restricted Circulation JTO Ph-II DNIT Overview of IPv6 2.9.6 ANYCAST Like multicast addresses, an anycast address identifies multiple interfaces on multiple devices. But there‘s a big difference: the anycast packet is delivered to only one device—actually, to the closest one it finds defined in terms of routing distance. And again, this address is special because you can apply a single address to more than one host. These are referred to as ―one-to nearest‖ addresses. Anycast addresses are typically only configured on routers, never hosts, and a source address could never be an anycast address. IETF did reserve the top 128 addresses for each /64 for use with anycast addresses. 2.9.7 SPECIAL IPV6 ADDRESS Like in case of IPv4 addresses are reserved for special purpose, in IPv6 as well addresses are reserved for special purpose as listed below. Special IPv6 Address Meaning This is the equivalent of IPv4‘s 0.0.0.0 and is typically the source address of a host before the host receives an IP addresswhen you‘re using DHCP-driven 0:0:0:0:0:0:0:0 Equals ::. stateful configuration. 0:0:0:0:0:0:0:1 Equals ::1. The equivalent of 127.0.0.1 in IPv4. This is how an IPv4 address would be written in a mixed 0:0:0:0:0:0:192.168.100.1 IPv6/IPv4 network environment. 2000::/3 The global unicast address range. FC00::/7 The unique local unicast range. FE80::/10 The link-local unicast range. FF00::/8 The multicast range. 3FFF:FFFF::/32 Reserved for examples and documentation. 2001:0DB8::/32 A Also reserved for examples and documentation. Used with 6-to-4 tunneling, an IPv4-to-IPv6 transition system. The structure allows IPv6 packets to be transmitted over an IPv4 network without the need to configure explicit 2002::/16 tunnels. Table 2. Special IPv6 Addresses JTO Ph –II Version 3.0 Aug 2021 Page 26 of 136 For Restricted Circulation JTO Ph-II DNIT Overview of IPv6 2.10 IPV6 ADDRESS ASSIGNMENTS OPTIONS: 2.10.1 MANUAL CONFIGURATION Network administrator can manually configure IPv6 address to routers interfaces. 2.10.2 STATELESS AUTOCONFIGURATION Stateless auto configuration requires no manual configuration of hosts, minimal (if any) configuration of routers, and no additional servers. The stateless mechanism enables a host to generate its own addresses. The stateless mechanism uses local information as well as non-local information that is advertised by routers to generate the addresses. Routers advertise prefixes that identify the subnet or subnets that are associated with a link. Hosts generate an interface identifier that uniquely identifies an interface on a subnet. An address is formed by combining the prefix and the interface identifier. In the absence of routers, a host can generate only link-local addresses. However, link-local addresses are only sufficient for allowing communication among nodes that are attached to the same link. 2.10.3 MODIFIED EUI-64 (EXTENDED UNIQUE ID-64) A 64-bit interface identifier is most commonly derived from its 48-bit MAC address. A MAC address 00-0C-29-0C-47-D5 is turned into a 64-bit EUI-64 by inserting FF-FE in the middle: 00-0C-29-FF-FE-0C-47-D5. When this EUI-64 is used to form an IPv6 address, it is modified: the meaning of the Universal/Local bit (the 7th most significant bit of the EUI-64, starting from 1) is inverted, so that a 1 now means Universal. To create an IPv6 address with the network prefix 2001:db8:1:2::/64 it yields the address 2001:db8:1:2:020c:29ff:fe0c:47d5 (with the Universal/Local bit, the second-least-significant bit of the underlined quartet, inverted to 1 in this case because the MAC address is universally unique). 2.10.4 STATEFUL AUTOCONFIGURATION In the stateful autoconfiguration model, hosts obtain interface addresses or configuration information and parameters from a DHCPv6 server. Servers maintain a database that checks which addresses have been assigned to which hosts. The stateful autoconfiguration protocol allows hosts to obtain addresses and other configuration information from a server. Stateless and stateful autoconfiguration complement each other. For example, a host can use stateless autoconfiguration to configure its own addresses, but use stateful autoconfiguration to obtain other information. 2.11 THE STRUCTURE OF AN IPV6 PACKET HEADER. The IPv6 packet as shown below is composed of two main parts: the header and the payload. The header is in the first 40 octets of the packet and contains both source and destination addresses (128 bits each), as well as the version (4-bit IP version), traffic class (8 bits, Packet Priority), flow label (20 bits, QoS management), payload length in bytes (16 bits), next header (8 bits), and hop limit (8 bits, time to live). The payload can be up to 64KiB in size in standard mode, or larger with a "jumbo payload" option. JTO Ph –II Version 3.0 Aug 2021 Page 27 of 136 For Restricted Circulation JTO Ph-II DNIT Overview of IPv6 Fragmentation is handled only in the sending host in IPv6: routers never fragment a packet, and hosts are expected to use PMTU discovery. The protocol field of IPv4 is replaced with a Next Header field. This field usually specifies the transport layer protocol used by a packet's payload. In the presence of options, however, the Next Header field specifies the presence of an extra options header, which then follows the IPv6 header; the payload's protocol itself is specified in a field of the options header. This insertion of an extra header to carry options is analogous to the handling of AH and ESP in IPsec for both IPv4 and IPv6. Figure 13: Structure of IPv6 Header 2.12 TRANSITION MECHANISM Until IPv6 completely supplants IPv4, which is not likely to happen in the foreseeable future, a number of so-called transition mechanisms are needed to enable IPv6-only hosts to reach IPv4 services and to allow isolated IPv6 hosts and networks to reach the IPv6 Internet over the IPv4 infrastructure contains an overview of the below mentioned transition mechanisms. 2.12.1 DUAL STACK Since IPv6 is a conservative extension of IPv4, it is relatively easy to write a network stack that supports both IPv4 and IPv6 while sharing most of the code. Such an implementation is called a dual stack, and a host implementing a dual stack is called a dual-stack host. Most current implementations of IPv6 use a dual-stack. Some early experimental implementations used independent IPv4 and IPv6 stacks. There are no known implementations that implement IPv6 only. JTO Ph –II Version 3.0 Aug 2021 Page 28 of 136 For Restricted Circulation JTO Ph-II DNIT Overview of IPv6 2.12.2 TUNNELING In order to reach the IPv6 Internet, an isolated host or network must be able to use the existing IPv4 infrastructure to carry IPv6 packets. This is done using a technique somewhat misleadingly known as tunnelling which consists in encapsulating IPv6 packets within IPv4, in effect using IPv4 as a link layer for IPv6. IPv6 packets can be directly encapsulated within IPv4 packets using protocol number 41. They can also be encapsulated within UDP packets e.g. in order to cross a router or NAT device that blocks protocol 41 traffic. 2.12.3 AUTOMATIC TUNNELING Automatic tunneling refers to a technique where the tunnel endpoints are automatically determined by the routing infrastructure. The recommended technique for automatic tunneling is 6to4 tunneling, which uses protocol 41 encapsulation. Tunnel endpoints are determined by using a well-known IPv4 anycast address on the remote side, and embedding IPv4 address information within IPv6 addresses on the local side. 6to4 is widely deployed today. Teredo is an automatic tunneling technique that uses UDP encapsulation and is claimed to be able to cross multiple NAT boxes. Teredo is not widely deployed today, but an experimental version of Teredo is installed with the Windows XP SP2 IPv6 stack. IPv6, 6to4 and Teredo are enabled by default in Windows Vista. 2.12.4 CONFIGURED TUNNELING Configured tunneling is a technique where the tunnel endpoints are configured explicitly, either by a human operator or by an automatic service known as a Tunnel Broker. Configured tunneling is usually more deterministic and easier to debug than automatic tunneling, and is therefore recommended for large, well-administered networks. Configured tunneling typically uses either protocol 41 (recommended) or raw UDP encapsulation. 2.12.5 PROXYING AND TRANSLATION When an IPv6-only host needs to access an IPv4-only service (for example a web server), some form of translation is necessary. The one form of translation that actually works is the use of a dual-stack application-layer proxy, for example a web proxy. 2.13 CONCLUSION An IPv6 address is a 128-bit alphanumeric value that identifies an endpoint device in an IPv6 network. IPv6 is the successor to a previous addressing infrastructure, IPv4, which had limitations IPv6 was designed to overcome. Notably, IPv6 has drastically increased address space compared to IPv4. JTO Ph –II Version 3.0 Aug 2021 Page 29 of 136 For Restricted Circulation