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CIS 153 Networking Essentials

CIS 153 Networking Essentials. Week 5 – Chapters 5 and 4. Before we start. Student Success Forms Remaining Article review sign ups Updates to the schedule Networking Essentials Research Webquest. Networking Essentials Research Webquest.

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CIS 153 Networking Essentials

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  1. CIS 153Networking Essentials Week 5 – Chapters 5 and 4

  2. Before we start • Student Success Forms • Remaining Article review sign ups • Updates to the schedule • Networking Essentials Research Webquest

  3. Networking Essentials Research Webquest • Project designed to provide real-world experience in specifying network components • This week: • Read research webquest instructions on Blackboard website • Participate in discussion postings and complete initial research online • Submit work-in-progress spreadsheet in your second discussion posting • Due by next Tuesday

  4. Chapter 5 Making Networks Work

  5. Why do I need to know this? • Applications are becoming more dependent on computer networks • Networks introduce a whole slew of potential problems that need to be troubbleshooted • Understand the services provided by the networking stack • Problems can crop up anywhere in the stack

  6. Layers • Read p.162

  7. Each layer has its own function • Think of it like object-oriented programming • Each layer calls on the functions of the one below it and above • The networking process as a whole is successful only on the completion of the entire process (that the data successfully was received) • More than the sum of its parts

  8. Layers 1-2 define the network’s physical media and signaling characteristics (physical) • Layers 3-4 move information from sender to receiver and handle the data to be sent or received (logical) • Layers 5-7 manage “conversations” across a network and deal with how data is prepared for applications or packaged for delivery across the network (logical)

  9. Each layer on one computer behaves as though it were communicating with its twin on the other computer • Called logical or virtual communication between peer layers

  10. Encapsulation • On its way up and down the stack, it is contained in what is called a protocol data unit (PDU) • Each layer adds its own header (sometimes a trailer as well)

  11. What does the Application layer do? • Provides interfaces for applications to access the network • PDU at this layer is called data • Some applications that tie in here are clients, others are servers • Example: Web browser on one end and web server on the other (HTTP) • Another example • Client for Microsoft Networks (client) • File and Printer Sharing for Microsoft Networks (server)

  12. What does the presentation layer do? • Handles data formatting for network communications • Converts data to and from a format that can survive network transmission • Handles protocol conversion, data encryption/decryption, compression (other side needs to support) • Redirector • Intercepts requests for files, printers, etc • Application layer and presentation layer are often combined together

  13. What does the session layer do? • Allows two parties to hold ongoing communications – called a “session” • Handles setup, data exchanges, and teardown • Monitors session identification so only designated parties participate • Some common functions found here: DNS, NetBIOS name resolution, logon and logoff functions such as FTP, Client for Microsoft Networks, and NFS

  14. What does the session layer do? • Inserts checkpoints in the data stream so that if packets are lost or corrupted only information transmitted after a checkpoint needs retransmission • Handles who can transmit and for how long • Maintains a connection by transmitting keep-alive messages that prevent disconnection because of no activity • Enforces how long a session can remain open/idle before disconnection

  15. What does the transport layer do? • Segments long data streams into chunks that match the maximum packet size for the networking medium • Includes error checks • Handles resequencing chunks into order • Handles flow control (destination computer is not overwhelmed with packets) • think fast server sending to dial-up client • Where TCP from TCP/IP lives • Where SPX from IPX/SPX lives • This layer covered in-depth next week

  16. What does the network layer do? • Handles addressing messages and translating logical addresses into MAC addresses • Determines how to route from sender to receiver based upon network conditions, Quality of Service, cost of alternate routes (assigned by network admin), and delivery priorities • Where routers and basic firewalls operate • Enforces access control (meet specified source or destination address)

  17. What does the network layer do? • PDU at this layer is called the packet • IP from TCP/IP operates at this layer • IPX form IPX/SPX operates at this layer • Problems that can be found at this layer include incorrect IP address or subnet mask (discussed next week) and incorrect router configuration.

  18. What does the Data Link layer do? • PDU called a frame • Consists of a header and trailer • Trailer contains error checking value called a Cyclical Redundancy Check (CRC) • CRC is created by a mathematical formula of the data bits in the rest of the data in the frame • If the data and the CRC match up, it is assumed that the frame arrived OK

  19. What does the Data Link layer do? • Header contains source and destination hardware (MAC) address • If destination computer is not directly reachable, the MAC address of the intermediary (router) is the destination address • If errors are detected (from CRC check), the frame is discarded • However, usually the transport layer has the responsibility of retransmitting the packet that had errors • The software component at this layer is the NIC driver, the hardware is the NIC • Switches also live at this layer

  20. What does the Physical layer do? • Converts bits into signals and signals into bits

  21. The Frame • Networks split data into small pieces because: • Networks would become saturated (other computers wouldn’t get a turn while someone was downloading a huge file) • “If one person talks nonstop for minutes on end, nobody else is able to join the conversation. However, if the speaker is polite and pauses occasionally between sentences, other people have an opportunity to speak.” • Networks can become unreliable • Retransmitting a small chunk is far faster then retransmitting an entire file

  22. Structure of a frame • Header contains address of sender, address of receiver, info containing frame size or content, an alert signal to indicate data transmission, and clocking information to synchronize transmission • Data section is called the “payload” – consists of data and headers from other layers (sized from 50 bytes to 16 Kbytes) • Trailer contains CRC • Note: most protocols (such as TCP/IP) add headers only to the Transport, Network, and Data Link Layers)

  23. Packet Data Units (PDU)’s

  24. Types of Data Frames • Unicast – to one computer • Broadcast – to all computers in a broadcast domain (subnet) • Routers usually suppress broadcast packets from traveling to other networks • Multicast – to computers listening to a particular shared network address

  25. IEEE 802 Specifications

  26. IEEE 802 Specifications

  27. 802 extensions to the OSI model • 802 actually was created four years before the OSI model • 802 broke the data link layer into two sublayers

  28. LLC sublayer and MAC sublayer • Logical Link Control (LLC) sublayer is the interface point for the network layer • Handles error recovery in some situations (carried out by hardware) • Media Access Control (MAC) sublayer manages access to the physical medium • Responsible for physical addressing • Physical address is burned into the ROM of every NIC and called a MAC address

  29. Hands-On Exercises • We will do together: • Hands-On Project 5-1 • Hands-On Project 5-3

  30. Chapter 4 Network Interface Cards

  31. Network Interface Card (NIC) • What does it do? • Establishes and manages the computer’s network connection • Translates digital computer data into signals appropriate for the network medium and vice versa • A computer’s internal bus is parallel while networks are serial • Why?

  32. Network Interface Card (NIC) • The NIC has a buffer on it to hold the information as it sends it out as serial or waits to receive enough information to send as parallel • The NIC packages the data it receives into what is called a frame, which is then sent out on the network • It similarly unpacks frames that it receives and sends that up the networking stack • At this layer, the data unit is called a frame not a packet

  33. Network Interface Card (NIC) • The NIC is also responsible for knowing when to send data and to listen for only what is addressed to it • That function can also be turned off (which is called Promiscuous mode) • Each NIC has a unique identifier, called a Media Access Control (MAC) address programmed on read-only memory (ROM) • It is by the MAC address that a computer knows that a frame is destined for that computer

  34. Busses • The main busses used for NIC’s are PCI for desktops and PCI-X and PCI express for newer servers • Can also use USB and PC Card • Learn more about busses in Computer Repair • If your adapter is not PnP, you will have to manually configure it • Even with integrated NIC’s, there is still plenty of need to install other NIC’s

  35. NIC characteristics • Slow NIC’s are one cause of poor network performance • See p.134-135 for others • Bus mastering • Co-processors • Some processors are available to offload IPSec (others offload SSL processing) • Quality of Service (QoS) • Doesn’t have to be on the card • Automatic Link Aggregation • Fault tolerance – NIC failover • Management – Wake on LAN, SNMP

  36. Wireless Adapters and PXE • Wireless adapters have additional issues to deal with • Use encryption • WEP has substantial security weaknesses • WPA is much better • Some NIC’s are PXE (preboot execution environment) compliant • Great for ghosting a computer (no CD or Floppy needed to boot the computer!) • Diskless workstations

  37. Drivers • The computer needs to know how to talk to the NIC • Bad drivers are the number one cause of serious crashes (BSOD) • Major network driver standards • NDIS – used by all Windows OS’s • Win32 Driver Model (WDM) – used on newer Windows OS’s, requires less driver code (generic class driver that manufacturer enhances) • Open Data-link Interface – similar to NDIS (allows multiple protocols) used by Apple and Novell

  38. Drivers and Configuration • New drivers available on manufacturers website • Knowledge Base is a great tool to find out how to fix common problems • Wireless NIC’s will have to be configured to the SSID (service set identifier) of the network you want to associate with • Many wireless networks broadcast theirs but some do not

  39. Hands-on exercises • We will do 4-2 and 4-4 together

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