Tag Archives: Troubleshooting TCP/IP

Network+ ( Troubleshooting TCP/IP)

Leave a reply

TCP/IP offers several tools that are helpful in the troubleshooting process and provide information to help locate and correct problems. Some of these are listed below:

  • ARP – Provides a mapping from the logical 32-bit TCP/IP address to the physical 48-bit MAC address (i.e. translates a IP address into MAC address).
  • TELNET – Provides a virtual terminal or remote login across the network that is connection-based and handles its own session negotiation. The remote server must be running a Telnet service for clients to connect. Defaults settings are Port 23 VT100 terminal emulation.
  • NBTSTAT – Is used to troubleshoot connectivity problems between 2 computers communicating via NetBT, by displaying protocol statistics and current connections. NBTSTAT examines the contents of the NetBIOS name cache and gives MAC address.
  • TRACERT – By sending out ICMP packets, it determines the path taken by a data packet to reach it’s destination and can help determine at what point a network connection is now longer active. Can help troubleshoot network response time issues.
  • NETSTAT – Displays in-depth detail about TCP/IP protocol status and statistics.
  • WINIPCFG – Displays current TCP/IP configurations on Windows workstations(see also IPCONFIG on Windows NT).
  • IPCONFIG – Below are the ipconfig switches that can be used at a command prompt.

    – ipconfig /all will display all of your IP settings.
    – ipconfig /renew forces the DHCP server, if available to renew a lease.
    – ipconfig /release forces the release of a lease.

  • PING – Uses ICMP to verify a connection to a remote host by sending echo requests and “listening” for reply packets.
  • NSLOOKUP – This tool queries a DNS database for information about DNS objects and can be used to troubleshoot name resolution problems.

General troubleshooting strategy includes the following steps:

  1. Establish the symptoms
  2. Identify the affected areas
  3. Establish what has changed
  4. Select the most probable cause
  5. Implement a solution
  6. Test the result
  7. Recognize the potential effects of the solution
  8. Document the solution

Basic TCP/IP troubleshooting steps include:

  1. Ping 127.0.0.1 – This is the loopback address and verifies that the computer that you are pinging from can communicate via TCP/IP with its own ethernet adapter.
  2. Ping own IP address – Verifies that a valid IP address was entered for this computer.
  3. Ping default gateway – Typically this would be the near side of a router. If you can ping this address, then you should be able to ping other hosts on your same subnet.
  4. Ping far side of router – This will verify that the routing table is correct.
  5. Ping remote host – If this works then it would appear that there are valid communications.
  6. If you are unable to connect to a host via host or domain name, see if you can connect to it using its IP address. If so, then you are likely having name resolution problems and should check your DNS configuration.

For the exam troubleshooting section, you will need to know how to solve various problems based on information such as PING/TRACERT/IPCONFIG output, topology type, operating system, network configuration, visual indicators (link lights, collision lights), etc. There will most likely be diagrams that you will have to glean information from.