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TCP/IP Basics

TCP/IP Basics. Alvin Kwan. What is TCP/IP?. It is a protocol suite governing how data can be communicated in a network environment, both local and globally.

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TCP/IP Basics

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  1. TCP/IP Basics Alvin Kwan

  2. What is TCP/IP? • It is a protocol suite governing how data can be communicated in a network environment, both local and globally. • To remind you what a protocol is, please read http://www.leapforum.org/published/internetworkMobility/split/node10.htmlto learn a particular protocol known as ARQ (automatic repeat request) protocol

  3. OSI vs. TCP/IP

  4. History of TCP/IP (1/2) • Stands for Transmission Control Protocol/Internet Protocol(TCP/IP) • Developed by Defense Advanced Research Projects Agency (DARPA) under the sponsorship of U.S. Department of Defense (DoD) in since late 1960s • 1972 – Telnet • 1973 – File Transfer Protocol (FTP) • 1974 – Transmission Control Protocol (TCP)

  5. History of TCP/IP (2/2) • 1980 – User Datagram Protocol (TCP) • 1981 – Internet Protocol (TCP) • 1982 – TCP/IP as a protocol suite • 1984 – Domain Name System (DNS) • 1991 – Transfer of funding responsibility from DAPRA to National Science Foundation (NSF), which started to turn the military originated protocols into civic use, notably in education sector

  6. Some TCP/IP features • It is an open standard, which is also adopted by the Internet. • It offers a routable protocol such that the path of every piece of data that moves through the network is traceable. • It adopts a single and simple addressing scheme which is easy to understand • IP is a connectionless protocol (with data transferred in individual packets); whereas TCP is connection-oriented.

  7. Connectionless vs. Connection-oriented Protocols (1/2) • Connectionless protocols • The data communication method occurs between hosts with no previous setup • Send data across the network to its destination without guaranteeing receipt • Higher layers handle packet sequencing and certain data integrity control issues • Fast; require little overhead • Most LAN protocols at the data link layer are connectionless • Data packets in a connectionless communication are referred to as datagrams More to follow …

  8. Connectionless vs. Connection-oriented Protocols (2/2) • Connection-oriented protocols • Establish a formal connection between two computers, guaranteeing the data will reach its destination • Higher layers can rely on low layers to handle matters of packet sequencing, data integrity, and delivery timeouts • Slower but more reliable • ATM networks are connection oriented at the data link layer

  9. Network Interface Layer (1/3) • Lowest layer in the TCP/IP stack • To define how a computer connects to a network • It does not regulate the type of network that the host is on and thus TCP/IP can be run on an Ethernet, Token Ring or Fiber Distributed Data Interface (FDDI) or any other network topology

  10. Network Interface Layer (2/3) • Physical (or MAC) address, which is burnt into every network interface card (NIC) • MAC address is usually represented in 12 hexadecimal digits (or 48 bits) • First six hexadecimal digits uniquely represent the manufacturer • Last six hexadecimal digits is a unique serial number that the card’s manufacturer has assigned to the NIC

  11. Network Interface Layer (3/3) • For a TCP/IP packet to be delivered, it must contain the destination node’s MAC address so that a host can check whether the packet is directed to it. • A broadcast packet is designed to be attended by all hosts and it has a target MAC address of FFFFFFFF, i.e., all bits set.

  12. The Internet Layer • The internal layer contains protocols for addressing and routing of packets. • Internet Protocol (IP) • Address Resolution Protocol (ARP) • Internet Control Message Protocol (ICMP) • Internet Group Message Protocol (IGMP) • Routing protocols (e.g., RIP)

  13. Internet Protocol (1/2) • To determine the source and destination IP addresses of every packet • Every host on a network is assigned a unique IP address (logical address) • IP address is divided into two parts: network number and host address on that network • Based on the subnet mask and IP address, it can be decided whether the target is a “remote” host or a “local” host (and details will be given later)

  14. Internet Protocol (2/2) • For a remote host, IP needs to send the packet through a gateway or a router (which is also identified by an IP address). • Connectionless and thus unreliable transmissiion

  15. Address Resolution Protocol (ARP) • Protocol to resolve an IP address to a physical address. • The hardware address will be cached for a short time. • To resolve an IP address to a physical address • Try the ARP cache (kept in RAM) • If not found in cache, initiate an ARP request broadcast and keep the result in cache • Try the command “ARP –A” in a command window

  16. ARP Command

  17. Internet Control Message Protocol (ICMP) • For sending error messages, performing diagnostics and controlling data flow • Try “ping cite.hku.hk” to test the network connection to another host

  18. Internet Group Message Protocol (IGMP) • IGMP enables one host to send one stream of data to many hosts at the same time with the use of a multicast address • Some routing protocols use IGMP to exchange routing tables

  19. Routing Protocols • Routing Information Protocol (RIP) • Simple IP-based routing protocol that collects and exchange information about network route and status • Only suitable for small networks • Open Shortest Path First (OSPF) • Typically used by routers to determine the best path through a network

  20. Transport Layer • Transmission Control Protocol (TCP) • Primary IP transport protocol • Connection-oriented and thus guarantee a more reliable delivery • Use port numbers to identify communicating applications • Responsible for message fragmentation and reassembly (with the use of sequence number) • User Datagram Protocol (UDP) • A connectionless transport protocol which runs faster continued

  21. TCP/IP Applications • Domain Name System (DNS) • For URL to IP-address translation • File Transfer Protocol (FTP) • Application protocol for file transfer and directory/file manipulation services • Telnet • For remote terminal sign-on • Simple Mail Transport Protocol (SMTP) • Provide messaging services (i.e., sending e-mails) continued

  22. IP Addressing • IP is responsible for addressing and routing in the TCP/IP environment • IP addresses • Logical addresses, which are 32 bits (4 bytes) long • A decimal number from 0 to 255, separated by periods, represents each byte or octet • Two sections • One defines the network a computer is on • One defines the host ID for a computer • Example: 172.24.206.18

  23. IP Addressing • Originally, three classes of IP addresses • Class A • Large corporations • ID numbers between 1 and 126 (in its first octet, or 8 bits) • Class B • Medium-sized networks • Network IDs between 128 and 191 (in its first octet, or 8 bits) • Class C • Small networks • Range from 192 to 223 (in its first octet, or 8 bits) • IP address registries manage the total collection of valid IP addresses

  24. IP Addressing • IP addresses are rapidly becoming scarce • TCP/IP’s technical governing body has reserved a series of addresses for private networks • IETF is working on a new implementation of TCP/IP (IPv6) that uses addresses that are 8 bytes long but retain backward compatibility with IPv4 4-byte addresses

  25. Classless Inter-domain Routing (CIDR) (1/2) • A more efficient way to assign IP addresses than using IP address “classes” • The network and host addresses boundary is not always made on octet boundaries, but may be made any specific number of bits from the beginning of the address • Steal bits from the network address for use in the host address and this is also called supernetting • A slash following IP address is used to indicate the number of bits of the network address, e.g., 192.203.187.32 /22

  26. Classless Inter-domain Routing (CIDR ) (2/2) • Advantages • Subnet ID may now be all 0’s or 1’s • Avoid of wasting a number of IP addresses when subnetting a Class C address • Disadvantages • Router support is needed • All possible bit patterns used for supernetting a network are to be reserved to be used by that network only

  27. Subnet Masks • The “all ones” bit pattern that masks the network portion of an IP address • Class A address default: 255.0.0.0 • Class B address default: 255.255.0.0 • Class C address default: 255.255.255.0

  28. Examples on Subnet Mask and Supernets • See pp203-205 of the recommended reading

  29. Dynamic Host Configuration Protocol (DHCP) • A TCP/IP protocol that allows automatic IP addresses and subnet mask assignment • Major benefit is ease with which computers can be moved • Not suitable for systems that require a static address, such as web servers • A dedicated host, which can be a router or a computer, to take the role of DHCP server

  30. Readings • http://www.wown.com/j_helmig/tcpip.htm • http://www.yale.edu/pclt/COMM/TCPIP.HTM • http://www.ii.uib.no/~magnus/TCP-1.html http://www.pcsupportadvisor.com/search/c04100.htm

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