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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 (IP) • 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 without prior arrangement with the recipient 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 over the network layer 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. Exercise: Finding Ethernet Card Manufacturer • Get the MAC address by executing “ipconfig /all” in a Microsoft command window. • Look for the first six hexadecimal digits of the physical address which is the Organizational Unique Identifier (OUI) • Go to http://standards.ieee.org/regauth/oui/index.shtmland use the OUI to check the Ethernet card manufacturer

  13. 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)

  14. 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)

  15. 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). • IP is connectionless and thus support an unreliable transmission

  16. Address Resolution Protocol (ARP) • Protocol to resolve an IP address to a physical address (see details in Wikipedia) • The hardware address will be cached for a short time (2-10 minutes). • 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

  17. ARP Command

  18. 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

  19. Ping Command

  20. 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 (which will be discussed later)

  21. Routing Protocols (More discussion on routing in another lesson) • 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

  22. 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

  23. Transmission Control Protocol • TCP adopts a 3-way handshake to establish a connection for data communication. • The client application sends a SYN to the server. • In response, the server replies with a SYN-ACK. • Finally the client sends an ACK (usually called SYN-ACK-ACK) back to the server.

  24. 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

  25. 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 (i.e. network ID) • One defines the host ID for a computer (i.e. host ID) • All devices on the same network share the same common network ID • Example: 172.24.206.18

  26. Classful Network (1/3) • Originally, three classes of IP addresses (which is obsolete on modern internet) • 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

  27. Classful Network (2/3)

  28. Classful Network (3/3) • The number of valid networks and hosts available is always 2N - 2 (where N is the number of bits used, and the 2 adjusts for the invalidity of the first and last addresses).

  29. Subnetting (1/2) • Subnetting allows a single larger network to have a number of smaller networks within it by allocating bits from the host portion as a network portion.

  30. Subnetting (2/2) • A subnet mask is made of a sequence of 1’s followed by a sequence of 0’s. • To reduce network traffic, routers are usually used to separate subnets. • Questions: • How many subnets can be formed in the previous example for a classful network? • What is the size of each subnet for a classful network in the previous example?

  31. Problem of Classful Network • The principal problem was that most sites were too big for a "class C" network number, and received a "class B" number instead. With the rapid growth of the Internet, the available pool of class B addresses was rapidly used up. • To solve the problem, classful network was replaced by classless inter-domain routing (CIDR) around 1993.

  32. Classless Inter-domain Routing (CIDR) • 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 • A slash following IP address is used to indicate the number of bits of the network ID, e.g., 192.203.187.32 /22 • Steal bits from the network address for use in the host address and this is also called supernetting

  33. Class Ranges

  34. Special Ranges of IP Address

  35. Supernetting Example

  36. Without Supernetting

  37. With Supernetting

  38. Pros and Cons of CIDR • 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 • Disadvantage • Router support is needed • Complexity

  39. Exercise: Network Calculator • Go to http://www.subnetmask.info/ to try to use the network calculator for computing the subnet mask.

  40. Why IPv6 • 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

  41. 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

  42. References • Relevant pages in Wikipedia • http://www.firewall.cx/supernetting-intro.php • 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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