CH 31.pdf

CHAPTER XXXI IP ADDRESSING - IPV4/ IPV6 31.0 An Internet Protocol address (IP address) is essential to each device connected to a computer network that uses the Internet Protocol for communication....

CHAPTER XXXI IP ADDRESSING - IPV4/ IPV6 31.0 An Internet Protocol address (IP address) is essential to each device connected to a computer network that uses the Internet Protocol for communication. It serves both network interface identification and location addressing. 31.1 The IP address space is managed globally by the Internet Assigned Numbers Authority (IANA), and by five regional Internet registries (RIRs) responsible in their designated territories for assignment to local Internet registries, such as Internet service providers, and other end users. 31.2 Two versions of IP addressing are in common use in the Internet today. The original version of the Internet Protocol is Internet Protocol version 4 (IPv4) which majority of users are familiar with. The next version of IP addresses is called IPv6. 31.3 IPv4 addressing Scheme 31.3.1 An IPv4 address has a size of 32 bits, which limits the address space to around 4.29 billion (232) addresses. Of this number, some addresses are reserved for special purposes such as private networks (~18 million addresses) and multicast addressing (~270 million addresses). 31.3.2 IPv4 addresses are represented in dot-decimal notation, consisting of four decimal numbers, each ranging from 0 to 255, separated by dots, e.g., 172.16.254.1 31.4 Sub-networks 31.4.1 IP networks may be divided into sub-networks. For this purpose, an IP address consists of two parts: the network prefix in the high-order bits and the remaining bits called the rest field or host identifier used for host numbering within a network. The subnet mask notation determines how the IP address is divided into network and host parts. Indian Railways Telecom Manual - 2021 Page 376 31.4.2 Subnet mask is a number that identifies the number of bits used for the network part of the IP address. Subnet mask is also represented as a 32 bit number. If n number of bits represent the network part of the address, its 32 bit representation is n one’s followed by (32 - n) zeroes. This may then be represented in dotted decimal notation. 31.5 Private addresses 31.5.1 Computers not connected to the Internet that communicate only with each other via TCP/IP, need not have globally unique IP addresses. Such private networks are widely used and typically connect to the Internet with network address translation (NAT), when needed. 31.5.1.1 Special IP address ranges that are used for special purposes are: 0.0.0.0/8 – addresses used to communicate with the local network 127.0.0.0/8 – loopback addresses 169.254.0.0/16 – link-local addresses (APIPA) The special purpose IP addresses cannot be used for networking. 31.5.1.2 Private/ Public IP addresses The IANA (Internet Assigned Numbers Authority) reserves the following IP address blocks for use as private IP addresses: 10.0.0.0 to 10.255.255.255 172.16.0.0 to 172.31.255.255 192.168.0.0 to 192.168.255.255 The above ranges of the IP addresses can be used by anyone for an Intranet network. Except private & special purpose IP addresses all IP addresses of class A, B & C are public or global IP addresses. 31.5.2 Private addressing scheme of Indian Railways 31.5.2.1 IPv4 Private addresses allotted by the Railway Board are being used in the Data networks of IR. The private address space chosen for these networks are 10.0.0.0/8. The IP addresses are then further divided as per allotment among various zones and divisions for each of the individual data networks. 31.5.2.2 The 10.0.0.0/8 network address has been further subnetted to 10.X.0.0/16 network by Railway board and allocated to Zonal Railways, divisions , RDSO,PSUs and Training Institutes. 31.5.3 Public IP address is required for giving access of any intranet service to the Public through internet 31.5.4 Private IPs are free and need not require any permission for using these IP addresses. Indian Railways Telecom Manual - 2021 Page 377 31.5.5 Private IP addresses within the same local network must be unique and cannot be repeated. 31.5.6 Private IP addresses cannot communicate in the public domain and are not able to use Internet services. In this case, the connection to the Internet is possible via NAT (network address translation) features of networking which logically replaces the private IP address with a public one. 31.5.7 For availability of Internet facility minimum one public IP address is must for any Intranet network. Through NAT at Intranet gateway level private IP addresses are logically hidden and public IP addresses represent the Intranet traffic like a mediator in public domain. 31.5.8 An Internet Service Provider(ISP) is a company that provides Internet access to organizations and home users. 31.5.9 ISPs are responsible for making sure you can access the Internet, routing Internet traffic, resolving domain names, and maintaining the network infrastructure that makes Internet access possible. 31.5.10 At Present RCIL is the ISP for Indian Railways. 31.5.11 All Railnet users are able to access internet service through public IP used at Gateway level of RCIL through NATing. 31.6 IPv6 addressing Scheme 31.6.1 In IPv6, the address size was increased from 32 bits in IPv4 to 128 bits, thus providing up to 2128 (approximately 3.403×1038) addresses. This gives virtually unlimited unique addresses for future use. 31.7 Important features of IPV6 31.7.1 Sufficient address space for the near future. 31.7.2 Enhanced security: IPSec (Internet Protocol Security) is built into IPv6 as part of the protocol. This means that two devices can dynamically create a secure tunnel without user intervention 31.7.3 Header improvements: the packed header used in IPv6 is simpler than the one used in IPv4. The IPv6 header is not protected by a checksum so routers do not need to calculate a checksum for every packet making transmission efficient. 31.7.4 No need for NAT: since every device has a globally unique IPv6 address, there is no need for NAT. Indian Railways Telecom Manual - 2021 Page 378 31.7.5 Stateless address auto configuration: IPv6 hosts can automatically configure themselves with an IPv6 address even without a DHCP server. 31.8 Addressing Scheme 31.8.1 The 128 bits of IPV6 is represented as 32 hexadecimal numbers arranged in 8 quartets of 4 hexadecimal digit separated by a colon":" 31.8.1.1 Not case sensitive for A, B, C, D, E and F 31.8.1.2 Omission of ZEROS 31.8.1.3 Leading zero in any quartet can be omitted. 31.8.1.4 Four successive zeros in a Quartet can be substituted by one zero. 31.8.1.5 Replacing Successive Fields of Zeros with "::” 31.8.1.6 Multiple quartet with zero can be represented as :: but only once in a address Example: 2001:0DB8:AC10:FE01:0000:0000:0000:0000 31.9 IPv6 Migration 31.9.1 IPv6 and IPv4 are not compatible. Migration from IPv4 to IPv6 will be done in near future. Until IPv6 completely supplants IPv4, which is not likely to happen in the foreseeable future, a number of so-called transition/migration mechanisms are needed so that both coexists and work together. Various Indian Railways Telecom Manual - 2021 Page 379  stakeholders will have to become thorough with the knowledge of IPV6 and the migration strategies. These trained man- power will handhold railways to migrate Railnet and other networks from IPv4 to IPv6 when the migration boom occurs. 31.9.2 There are basically 3 methods for migrating from IPv4 to IPv6 that are prevalent today. 31.9.2.1 Dual Stack Method 31.9.2.1.1 It allows IPv4 & IPv6 to coexist in the same device & network. 31.9.2.1.2 In the dual stack method all the devices like PCs, switches, routers, ADSL modems etc. dual stacked i.e. these equipment will use both IPv4 drivers as well as IPv6 drivers. This will allow both IPv4 and IPv6 to coexist and gradual transition from IPv4 to IPv6 can happen. Here, the computer decides whether to use IPv4 or IPv6 based on sets of rules. DNS servers are also used to decide if IPv6 or IPv4 is used. Indian Railways Telecom Manual - 2021 Page 380 31.9.2.2 Tunneling 31.9.2.2.1 It allows IPv6 hosts to communicate over IPv4 infrastructure.Tunneling encapsulates IPv6 traffic within IPv4 packets.Allows isolated IPv6 end system and routers to communicate without the need to upgrade the IPv4 infrastructure that exists between them. 31.9.2.2.2 Following tunneling configurations exist: Router-to-Router Host-to-Router and Router-to-Host Host-to-Host Indian Railways Telecom Manual - 2021 Page 381 31.9.2.3 Translation [SIIT and NAT64] (Stateless IP/ICMP Translation) 31.9.2.3.1 In the SIIT and NAT64 method all the devices like PCs, switches, routers, ADSL modems etc. are configured with IPv6 address only, the gateways are configured with SIIT and NAT64 protocol and with DNS- 64, the gateways will connect external IPv4 as well as IPV6 network. 31.9.2.3.2 This allows communication between IPv4 only and IPv6 only end stations. The job of the translator is to translate IPv6 packets into IPv4 packets by doing address and port translation and vice versa. 31.9.2.3.3 This method seems to be the most preferred method to migrate IPv4 to IPv6. -x-x-x- Indian Railways Telecom Manual - 2021 Page 382