TCP/IP Basics

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TCP/IP Basics

• Alvin Kwan

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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/internetworkMob
  ility/split/node10.html to learn a particular
  protocol known as ARQ (automatic repeat request)
  protocol

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OSI vs. TCP/IP
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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)

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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

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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.

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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
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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

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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

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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 cards manufacturer has assigned
  to the NIC

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Network Interface Layer (3/3)

• For a TCP/IP packet to be delivered, it must
  contain the destination nodes 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.

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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)

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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)

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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

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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

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ARP Command
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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

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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

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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

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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
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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
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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

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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

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IP Addressing

• IP addresses are rapidly becoming scarce
• TCP/IPs 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

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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

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Classless Inter-domain Routing (CIDR ) (2/2)

• Advantages
• Subnet ID may now be all 0s or 1s
• 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

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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

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Examples on Subnet Mask and Supernets

• See pp203-205 of the recommended reading

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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

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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