Chapter 5 : The Internet: Addressing & Services

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Topic 6: Network Layer - Chapter 5 : The Internet: Addressing & ServicesBusiness Data Communications, 4e


Internet Addressing32-bit global internet address Includes network and host identifiers Dotted decimal notation 11000000 11100100 00010001 00111001 (binary) (decimal)


Types of addressesAddress Example Software Example Address Application Layer Web browser Network Layer TCP/IP Data Link Layer Ethernet 00-A0-C9-96-1D-90


AddressingThe network layer determines the best route through the network to the final destination. Based on this routing, the network layer identifies the data link layer address of the next computer to which the message should be sent.


Assigning AddressesIn general, the data link layer address is permanently encoded in each network card, and as part of the hardware that cannot be changed. Network layer addresses are generally assigned by software. Every network layer software package usually has a configuration file that specifies the network layer address for that computer.


Assigning AddressesApplication layer addresses (or server addresses) are also assigned by a software configuration file. Virtually all servers have an application layer address, but most client computers do not. Network layer addresses and application layer addresses go hand in hand. ( - means at the network layer.)


*How IP Addresses DistributedInternet Corporation for Assigned Names and Numbers (ICANN) oversees the Internet Assigned Numbers Authority (IANA) and controls how the Net's 4.29 billion IP addresses are used. IANA distributes address space to three geographically diverse Regional Internet Registries (RIRs) and encourage three RIRs to operate so that addresses remain unique, are mapped efficiently, and are treated as a precious resource. Three RIRs dole out available pools of IP based on a shared criteria. All deploy numerical address space to ISPs, local registries, and in some cases small users.


IP Address AllocationIANAInterNIC AmericaRIPE EuropeAPNIC AsiaNationalRegionalConsumer


Three RIRsAmerican Registry for Internet Numbers (ARIN) Reseaux IP Europeen (RIPE) Asia Pacific Network Information Centre (APNIC)


Internet AddressesInterNIC is responsible for network layer addresses (IP addresses) and application layer addresses or domain names ( There are five classes of Internet addresses. Classes A, B, and C are available to organizations Class D and E are reserved for special purposes and are not assigned to organizations.


Internet Address ClassesClass A (/8 address) The first digit is fixed, ranging 1-126 (01-7E), 16 million addresses 127.x.x.x is reserved for loopback Class B (/16 address) First two bytes are fixed with the first digit ranging 128-191 (80-BF), 65,000 addresses. Class C (/24 address) First 3 bytes are fixed, with the first digit ranging 192-223 (C0-DF), 254 addresses. Class D & E The first digit is 224-239 (E0-EF) and 240-255 (F0-FF) respectively. Reserved for special purposes and not available to organizations.


Internet Address Classes1/211261/41281911/8192 2231/161/16240 255Class CClass D Class EClass BClass ARanges of the first byte for different classes:Class A: 0xxxxxxx Class B: 10xxxxxx.xxxxxxxx Class C: 110xxxxx.xxxxxxxx.xxxxxxxx Class D: 1110xxxx.xxxxxxxx.xxxxxxxx Class E: 1111xxxx.xxxxxxxx.xxxxxxxx224 239Note: The IP addresses with the first byte as 0 and 127 are reserved


Internet Address Classes # of Addresses Class Available Addr-Structure Example Available # Class A 16 million First byte fixed 50.x.x.x 126 Organization assigns last three bytes Class B 65k First two bytes fixed 128.192.x.x 16k Organization assigns last two bytes Class C 254 First three bytes fixed 192.1.56.x 2 millions Organization assigns last byte


Internet AddressesThe Internet is quickly running out of addresses. Although there are more than 1 billion possible addresses, the fact that they are assigned in sets (or groups) significantly restricts the number of usable addresses. The IP address shortage was one of the reasons behind the IPv6, providing in theory, 3.2 x 1038 possible addresses. How to apply for IP address?


SubnetsAssign IP addresses to specific computers so that all computers on the same local area network have a similar address. Each LAN that is logically grouped together by IP number is called a TCP/IP subnet. Benefit: allows it to be connected to the Internet with a single shared network address an necessary use of the limited number of network numbers Overload Internet routing tables on gateways outside the organization




Subnet MaskSubnet mask enables a computer to determine which computers are on the same subnet. This is very important for message routing. E.g. IP address: Subnet mask: IP address: 129.118.49.x is for the computers in the same subnet


SubnetSubnet with partial bytes addresses. E.g. to Subnet mask: Subnet address: Subnet broadcast address:


Subnet IP address: 1000 0001.0111 0110.0011 0001.0110 1111 Subnet mask: 1111 1111.1111 1111.1100 0000.0000 0000 The IP prefix 1000 0001.0111 0110.00 Destination IP: 1000 0001.0111 0110.0011 0011.0110 1111 Destination IP: 1000 0000.0101 0011.0111 1111.0000 0001


Subnet Mask Template 0 0 1 0 1 1 01500 0 0 0 0 0 0 10 0 0 0 0 0 0 00 0 0 0 0 0 0 0100Network ID–Class BHost AddressPossible Subnet Address128255255Broadcast Address 128 64 32 16 8 4 2 1Mask Numbers


Dynamic AddressingAn address assignment problem: Each time the computer is moved, or its network is assigned a new address, the software on each individual computer must be updated. Solution: dynamic addressing With this approach, a server is designated to supply a network layer address to a computer each time the computer connects to the network.


Dynamic Addressing Two standards for dynamic addressing are commonly used in TCP/IP networks: Bootstrap Protocol (bootp) for dial-up networks (1985) Dynamic Host Control Protocol (DHCP) for non-dial-up networks (1993)


Dynamic AddressingThe Bootp or DHCP server can be configured to assign the same network layer address to the computer each time it requests an address or it can lease the address to the computer by picking the “next available” network layer address from a list of authorized addresses. Dynamic addressing greatly simplifies network management in non-dial-up networks too.


Address ResolutionAddress resolution: The sender translates the application layer address (or server name) of the destination into a network layer address; and in turn translates that into a data link layer address. Two approaches used in TCP/IP: Server address resolution Data link layer address resolution.


DomainA domain refers to a group of networks that are under the administrative control of a single entity, such as a company.


Server Name ResolutionDomain Name Service (DNS) Used for translating application layer addresses into network layer addresses. InterNIC Keeps the name and IP addresses of the name server that will provide DNS information for your address classes.

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Last Updated: 8th March 2018

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