OSI Troubleshooting
Troubleshooting TCP/IP

Basic troubleshooting for TCP/IP on Windows machines combines facts gathered from a router, switch, bridge, and AP perspective and facts gathered from a Windows client or server perspective. Some of the common TCP/IP connectivity problems are shown in Figure .

Ping
One of the most common ICMP uses is as a diagnostic tool. A simple ping utilizes ICMP to determine whether or not a host is receiving packets. For more details on ICMP, refer to RFC 792. A loopback ping is one of the first ping tests that should be performed when connectivity is in question. A loopback ping is addressed to 127.0.0.1, the loopback address, to check the local TCP/IP stack integrity and NIC.

ARP
ARP will display the IP to MAC address mapping. To view the ARP cache, at the command prompt type arp –a.

Ipconfig or Winipcfg
Ipconfig for Windows NT, 2000, or XP, or winipcfg for Windows 95 or 98 can be used to check the local host configuration. Enter a Command Prompt window on the host and enter the ipconfig /all command. The results of this command show the TCP/IP address configuration, including the address of the Domain Name System (DNS) server. If any IP addresses are incorrect or if no IP address is displayed, determine the correct IP address and edit it or enter it for the local host. The command ipconfig /release followed by ipconfig /renew will force a request to the DHCP server for an IP address.

Tracert
The tracert tool on a Windows NT, 2000, or XP host reports each node a TCP/IP packet crosses on its way to a destination. It does essentially the same thing as the trace command in the Cisco IOS Software.


Lab Activity

Lab Exercise: Troubleshooting TCP/IP Issues

In this lab, standard TCP/IP commands are utilized to troubleshoot connectivity problems between the wireless client and the AP.