Semester 1 v3.1.1: Networking Basics

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Semester 1 v3.1.1Networking Basics

• MODULE 11
• TCP/IP Transport and Application Layer

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Transport Layer Basics

• Segments data from upper layers, transported from
  source to destination over same data stream.
• Uses port numbers to distinguish upper-layer
  destination.
• Quality of service
• Flow control
• How fast the hosts are talking to each other.
• Congestion avoidance and control.
• Reliability
• Re-transmission of corrupted or lost data.
• Uses mechanisms such as sliding windows,
  sequencing numbers, acknowledgments.
• Transport Layer protocols
• TCP Transmission Control Protocol
• UDP User Datagram Protocol

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Getting the Message

• Establishes, maintains, terminates sessions
  between hosts.
• Dialogue control
• Is it Host A or Host Bs turn to send data?
• Two-Way Alternate
• Two-Way Simultaneous

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TCP Three-Way Handshake

• Mechanism to establish a session and synchronise
  sending and receiving hosts.
• Sequence of synchronise (SYN) and acknowledgement
  (ACK) segments.

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TCP Windowing

• TCP uses acknowledgements to ensure packets are
  delivered in the same order as they were sent.
• Window size defines the number of packets to be
  received before an acknowledgement is sent.

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Port Numbers

• Port numbers keep track of different
  conversations across the network.
• Common TCP ports
• FTP on ports 20 and 21
• Telnet on port 23
• SMTP on port 25
• HTTP on port 80
• Common UDP ports
• DNS on port 53
• DHCP on ports 67 and 68

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Transmission Control Protocol

• Connection-oriented
• Establishes a virtual link between hosts before
  transmission of data occurs.
• TCP Three-Way handshake
• Reliable
• Ensures destination receives all data
  eventually!
• Divides data into segments at source and gives
  them sequence numbers, re-assembles segments in
  order at destination, acknowledges receipt of
  data.
• Paired up with lower-layer Internet Protocol to
  form TCP/IP suite.

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User Datagram Protocol

• Connectionless
• No virtual link established before communication.
• Unreliable
• No guarantee that destination receives all data
  intact.
• No acknowledgements by the destination that it
  may have received any data.
• No flow control services.

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Application Layer Basics

• Layer 7 of the OSI model, Layer 4 of the TCP/IP
  model closest to users.
• Supports the communications components of
  applications.
• Provides a user interface to the lower layers of
  the OSI and TCP/IP models
• Direct Web browser, E-mail client, FTP client.
• Indirect Word processor, Spreadsheet, etc.
• When the user wishes to use the network, they
  must do so via the application layer.

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I want to be connected!

• We can find hosts on networks using
• IP address
• And just how many IP addresses do you know off by
  heart???
• NetBIOS name (Network Basic I/O System)
• Flat naming scheme on older Windows networks,
  usually used in conjunction with WINS servers.
• Suitable for a small LAN, but not feasible on the
  wider Internet.
• To make things easier, DNS was developed.

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Domain Naming System

• Uses characters and digits to form a recognisable
  domain name instead of using pure numbers.
• Effectively a distributed database to map between
  hostnames and IP addresses.
• Hierarchical naming system.
• Developed for human convenience rather than
  computer efficiency
• WinSock applications connect to other computers
  over TCP/IP using the IP address.

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DNS Namespace

• Hierarchical namespace is flexible.
• Many computers can have the same name.
• Provided the hierarchy level is different.
• Therefore, every Fully Qualified Domain Name must
  be unique.
• FQDN comprises the computers host name and its
  domain membership name.

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DNS Hierarchy

• Top of DNS hierarchy is the Root domain 13
  servers globally maintained by ICANN
• Next level down are top-level domains.
• .com, .org, .edu, .gov, .net, .au, .uk, .tw
• Second-level domains
• sun.com, whitehouse.gov, edu.au, cisco.com
• Third-level domains
• java.sun.com, uts.edu.au, tools.cisco.com

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FQDNs

• Compare these DNS addresses
• www.uts.edu.au
• www.it.uts.edu.au
• www.eng.uts.edu.au
• All computers have identical
• Hostname www
• Top-level domain au
• Second-level domain edu
• Third-level domain uts
• Difference is the fourth-level domain.

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Show me the website!!!

• Dont recall IP addresses, just the DNS address!
  Behind every DNS address is an IP address.
• Cisco Systems
• www.cisco.com 198.133.219.25
• Sun Microsystems
• www.sun.com 72.5.124.61
• Renault F1 Team
• www.renaultf1.com 81.20.128.10
• Sydney FC
• www.sydneyfc.com 144.140.78.207

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DNS Resolution

• Humans deal with domain names.
• Computers deal with IP addresses.
• A translator is required to resolve the DNS
  hostname to an IP address.
• The answer is DNS hostname resolution.

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DNS Hostname Resolution

• Domain info stored in zone database files.
• Forward Lookup Zone
• Resolves hostnames to IP addresses.
• All queries are examined and executed from right
  to left.
• Reverse Lookup Zone
• Resolves IP addresses to hostnames using the
  in-addr.arpa domain.
• Results of all queries to DNS servers are cached
  for later use.

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Welcome to my world )

• Daniel Comarmond
• CCNP, CCDP, CCSP, CCAI
• Cisco Networking Academy Instructor
• Systems Engineer Cisco Systems
• E-Mail dcom_at_it.uts.edu.au
• MSN dcom82_at_dcom82.com
• Phone [phone]
• Website http//www-staff.it.uts.edu.au/dcom
• Take care, and SMILE!!! )