Troubleshooting TCP/IP Configuration

A valid network device require proper network configuration in order to communicate with other local or remote devices. One of the most used

internet protocol is the TCP/IP protocol. So it is very important identifying and troubleshooting TCP/IP configuration problem. Once you identify

the problem is at TCP/IP stage. The two main problems are TCP/IP configuration and software interference.

Peaces of information required for a device in order to be network ready are:

1. IP address is consist of 32 digit binary number that identify your device from all other host with in the network.

2. Subnet mask is indicating the size of the network.

3. Default gateway address is a device on a network that serves as access point to other networks.

These are information that are needed in order to troubleshoot TCP/IP configuration problems successfully. Some of the tools that are

important for troubleshooting TCP/IP configuration are ipconfig, ping, and tracer command that are available on Windows.

Ipconfig command:

It display TCP/IP configuration value such as IP address, subnet mask and default gateway. It also display connection specifications for

domain name service (DNS). To open Windows terminal window, choose Start> Run, enter cmd, and click OK then type ipconfig at

command prompt and press return key.

Example of ipconfig command output.

C:\>ipconfig

Windows IP Configuration Ethernet adapter Local Area Connection:

       Connection-specific DNS Suffix  . : hsd1.mn.comcast.net.
       IP Address. . . . . . . . . . . . : 75.72.216.120
       Subnet Mask . . . . . . . . . . . : 255.255.248.0
       Default Gateway . . . . . . . . . : 75.72.216.1

If ipconfig command displays proper TCP/IP configuration value it shows that the local host is internet ready.

Ping and tracert command:

Ping loopback address: Open Windows terminal window. In order to check weather the TCP/IP configured properly installed on the host device ping the loopback address (127.0.0.1). That can tell you if the host is internet ready.

Example of ping loopback address output.

C:\>ping 127.0.0.1

Pinging 127.0.0.1 with 32 bytes of data:

Reply from 127.0.0.1: bytes=32 time<1ms TTL=128

Ping statistics for 127.0.0.1:

Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),

Approximate round trip times in milli-seconds:

Minimum = 0ms, Maximum = 0ms, Average = 0ms

The output shows that four ICMP packets with each 32 bytes in size sent and replayed from 127.0.0.1 address. TTL =128 indicates that the

number of hops remaining before the ping packet dropped.

If ping loopback address fails and not responding one or more of these are true.

       . No network card or bad network card.

       . TCP/IP driver corrupted.

       . Other hard ware or software interference.

If ping loopback succeed go to the next step.

Ping IP address: Ping back your host IP address verifies that the host configured with network. It forwards the packet to the loopback

address. Ping a local host successfully shows that your computer is communicating with other local hosts.

If you can’t ping other local hosts and you can ping the loopback address check whether your IP address is a valid IP address.

Ping the Default gateway address: Ping default gateway successfully shows that your host is connected to default gateway device and

also connected to other local host with in the same subnet as your device. If it fails, do one or all of the followings.

. Check if your host is configured with the right default gateway address.

. Check the physical connection between your host and default gateway device.

. Check if default gateway device is working.

Ping remote host: If you ping remote host successfully that verifies your local host can communicate with remote host through default

gateway device. If you can ping default gateway address but not remote host, use some of the options like -w to delay waiting time for each

reply and -n option to specify the number of echo requests to send. If still not responding, you can use the tracert command. The tracert

command can give important clues of each hops on path to the remote host. So, from the output of tracert command you can determine if

the remote host is not responding or one or more hops are down on the path to the remote host.

Example of tracert output.

C:\tracert www.cisco.com

Tracing route to origin-www.cisco.com [72.163.4.161] over a maximum of 30 hops:

1 12 ms 1 ms 1 ms 10.1.15.254

2 7 ms 3 ms 1 ms 172.16.252.174

3 4 ms 5 ms 3 ms cob-ole-Gi0-2-440.r.state.mn.us [207.171.87.82]

4 2 ms 6 ms 4 ms umn-scuhub-Te3-4-2005.r.state.mn.us [207.171.116 .189]

5 2 ms 4 ms 2 ms umn-scuhub-Te3-4-2005.r.state.mn.us [207.171.116 .189]

6 4 ms 5 ms 4 ms umn-lena-Te3-1.r.state.mn.us [207.171.116.126]

7 7 ms 5 ms 3 ms telecomb-gr-01-te-2-2-3000.northernlights.gigapo p.net [146.57.252.214]

8 3 ms 3 ms 4 ms mtc-gr-01-te-3-1.northernlights.gigapop.net [146 .57.252.134]

9 26 ms 8 ms 4 ms 66.162.50.105

10 17 ms 14 ms 20 ms peer-02-so-0-0-0-0.chcg.twtelecom.net [66.192.24 4.20]

11 33 ms 31 ms 30 ms cr2.cgcil.ip.att.net [12.122.132.134]

12 31 ms 30 ms 31 ms cr2.sl9mo.ip.att.net [12.122.2.22]

13 33 ms 32 ms 32 ms cr2.kc9mo.ip.att.net [12.122.28.89]

14 35 ms 31 ms 35 ms cr1.dlstx.ip.att.net [12.122.28.85]

15 34 ms 30 ms 30 ms cr83.dlstx.ip.att.net [12.123.18.109]

16 32 ms 35 ms 30 ms gar28.dlstx.ip.att.net [12.123.18.33]

17 31 ms 30 ms 31 ms 12.91.193.190

According to the example you can tracert to remote host name and the name can be resolved to destination hosts IP address. The tracert

returns a list of hops along the path to the destination.

Ping the host name of remote host: You can ping host name such as www.cisco.com and www.google.com to verify that you can resolve

a remote host name. If you ping remote host address successfully but not remote host name, the problem is with address resolution not with

network connectivity. Verify that the DNS server address are configured for the host at the property of TCP/IP configuration. Use the

ipconfig/all command to list the DNS server address. Then ping DNS server address to check if it is accessible.

The error messages that appear when you use ping command:

. Request timed out - It is a valid address but no reply from destination host. If the destination is local host, the most likely cause is firewall.

If the destination is a remote host, the Echo Reply messages were not received with in the timeout period. By default, the timeout period is

four seconds. You can use ping -w command option to increase the timeout period. Otherwise you can use tracert command to identify the

hop that is not responding.

. Unknown host name - The computer name doesn’t exist on local network. Make sure that the NetBios is enabled at TCP/IP property.

. Destination host unreachable - The default gateway can’t access the destination address. Either there is no default gateway or wrong

destination IP address.

Troubleshooting TCP/IP Configuration

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