Troubleshooting the Network

How To Troubleshooting The Network

Recognize the following steps as a systematic approach to identifying the extent of a network problem and, given a problem scenario, select the appropriate next step based on this approach:
   1. determine whether the problem exists across the network,
   2. determine whether the problem is workstation, workgroup, LAN or WAN,
   3. determine whether the problem is consistent and replicable, and
   4. use standard troubleshooting methods.

Identify the following steps as a systematic approach for troubleshooting network problems and, given a problem scenario, select the appropriate next step based on this approach:
   1. identify the exact issue,
   2. recreate the problem,
   3. isolate the cause,
   4. formulate a correction,
   5. implememt the correction,
   6. test,
   7. document the problem and the solution, and
   8. give feedback.

Identify the following steps as a systematic approach to determining whether a problem is attributable to the operator or the system and, given a problem scenario, select the appropriate next step based on this approach:
   1. have a second operator perform the same task on an equivalent workstation,
   2. have a second operator perform the same task on the original operator's workstation,
   3. see whether operators are following standard operating procedure.

Given a network troubleshooting scenario, demonstrate awareness of the need to check for physical and logical indicators of trouble, including
   • link lights
   • power lights
   • error displays
   • error logs and displays
   • performance monitors.

Identify common network troubleshooting resources, including
   • knowledge bases on the World Wide Web
   • telephone technical support
   • vendor CDs.

Given a network problem scenario, including symptoms, determine the most likely cause or causes of the problem based on the available information. Select the most appropriate course of action based on this inference. Issues that may be covered include
   • recognizing abnormal physical conditions
   • isolating and correcting problems in cases where there is a fault in the physical media (patch cable)
   • checking the status of servers
   • checking for configuration problems with DNS, WINS, HOST file
   • checking for viruses
   • checking the validity of the account name and password
   • rechecking operator logon procedures
   • selecting and running appropriate diagnostics.

Specify the tools that are commonly used to resolve network equipment problems. Identify the purpose and function of common network tools, including
   • crossover cable
   • hardware loopback
   • tone generator
   • tone locator (fox and hound).

Given a network problem scenario, select appropriate tools to help resolve the problem.


Basic Knowledge
Define the layers of the OSI model and identify the protocols, services, and functions that pertain to each layer.

Application - (layer 7) Allows applications to use the network. Handles network access, flow control and error recovery. messages are sent between layers
   • Protocols - SMB, NCP
   • Services - Telnet, FTP use TCP, TFTP, NFS, SNMP, SMTP use TCP
   • Functions - User interface with applications & Gateways

Presentation - (layer 6) Translates data into a form usable by the application layer. The redirector operates here. Responsible for protocol conversion, translating and encrypting data, and managing data compression. messages are sent between layers
   • Protocols - NCP
   • Services - Telnet, FTP use TCP, TFTP, NFS, SNMP, SMTP use TCP
   • Functions - Gateways

Session - (layer 5) Allows applications on connecting systems to establish a session. Provides synchronization between communicating computers. messages are sent between layers
   • Protocols - N/A
   • Services - Telnet, FTP use TCP, TFTP, NFS, SNMP, SMTP use TCP
   • Functions - Gateways

Transport - (layer 4) Responsible for packet handling. Ensures error-free delivery. Repackages messages, divides messages into smaller packets, and handles error handling. segments of message fragments are sent between layers
   • Protocols - SPX, TCP, UDP and NetBEUI function on this layer
   • Services - TCP/SPX - connection-oriented communication for applications to ensure error free delivery; UDP - connectionless communications and does not guarantee packet delivery between transfer points
   • Functions - Gateways function on this layer

Network - (layer 3) Translates system names into addresses. Responsible for addressing, determining routes for sending, managing network traffic problems, packet switching, routing, data congestion, and reassembling data. Datagrams are sent between layers
   • Protocols - IPX, IP, ICMP, ARP, RARP, RIP, OSPF, EGP, IGMP, NetBEUI, DLC, and DecNET function on this layer
   • Services - software & hardware addresses and packet routing between hosts and networks (IP/IPX); software addresses to hardware addresses are resolved (ARP/RARP), sends messages and reports errors regarding packet delivery (ICMP), reports host group membership to local multicast routers (IGMP)
   • Functions - Routers and Brouters function up to this layer

Data link - (layer 2) Sends data from network layer to physical layer. Manages physical layer communications between connecting systems. Data frames are sent between layers
   • Protocols - HDLC (High-level Data Link Control); Supports asynchronous and synchronous transmissions. Uses LLC flow control
   • Services - Ethernet, Token Ring, and other communications occur here via frames. LLC - (802.2) Manages link control and defines SAP's (Service Access Points). MAC - (802.3, 802.4, 802.5, 802.12) Communicates with adapter card.
   • Functions - Switches, brouters and bridges function on this layer using the MAC sublayer

Physical - (layer 1) Transmits data over a physical medium. Defines cables, cards, and physical aspects. Data bits are sent.
   • Protocols - No protocols function on this layer
   • Services - Ethernet (CSMA/CD), Token Ring (token passing), and other communications occur
   • Functions - Repeaters and multiplexers function on this layer; bits are sent across the wire