Network Connectivity Testing commands

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Index

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ping

telnet

tracert

nslookup 

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ping
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The ping command verifies connectivity by sending Internet Control Message Protocol (ICMP) echo packets to a host and listening for an echo reply. 

Times on the Internet can range from 80ms (milliseconds) to 250ms, which is considered normal during peak hours. 

You can use the ping utility to test both the host name and IP address of the host for DNS resolution. 

A successful IP ping and failed host name ping could indicate name resolution issues. 

Example:
ping www.domain.com
ping 123.123.123.123

ping options
–t: continuous echo requests to a host. 
ping 123.123.123.123 –t

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telnet

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The Telnet command is used to test a variety of services for connectivity. 

You can use it to test for SMTP, SQL or Remote Desktop connectivity. 

This is a good test to use for service or port blocks resulting from a firewall configuration.

Usage

telnet <server> <port>

Example:

telnet mail.domain.com 25

telnet 123.123.123.123 3389

The response of a successful connection will be different for each service, but a failed connection will always respond with a variation of the following message: 

"Could not open connection to the host, on port n: Connect failed"

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Trace Route 

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A Trace Route command displays the path a packet takes to reach a destination from the machine that it is executed on. 

It does this by sending Internet Control Message Protocol (ICMP) echo request messages to the destination. The path is displayed as a list in the order of which it heard back from each node that it passed through on its way to the destination. 

The numbers on the trace show the time it's taking to travel to each of those locations. 

Times on the Internet can range from 80ms (milliseconds) to 250ms.

A Trace Route will include at least 4 pieces of information for each hop; the number of the hop, the Round Trip Time (RTT is displayed in milliseconds or ms) it takes to get from the interface of the current hop and then back again to your machine, the IP address of the interface for that hop and the hostname corresponding to the IP address of the hop. 

The default is to send out 3 packets to each hop. This is done in case a packet is lost and allows you to get an idea of whether or not there is a variance in the time for a specific hop.

A high number on the first external hop from you machine is a good indication of possible Local Area Network (LAN) issues.

An asterisk (*) indicates an echo request that was lost. 

These can be the result of security implementations of firewalls or Access Control List (ACL’s). 

Additionally, routers may be configured not to respond to this type of traffic. You may see a row of three asterisks with no IP address or hostname. The trace may then continue responding normally again and display the destination results.

Windows Usage

tracert domain.com 

tracert 123.345.567.789 

You can see the output results in the following example:

Tracing route to domain.com over a maximum of 30 hops:

  1    <1 ms    <1 ms    <1 ms  111.111.111.111

  2    <1 ms    <1 ms    <1 ms  222.222.222.222

  3     1 ms     1 ms     1 ms  111.222.111.222

  4     1 ms     1 ms    12 ms  222.111.222.111

  5     *        *        *     Request timed out.

  6    14 ms    13 ms    13 ms  domain.com

Trace complete.

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nslookup

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The Nslookup command allows you to displays information that you can use to diagnose Domain Name System (DNS) infrastructure. 

It is helpful when you want to query a specific DNS record.

Command Usage:

1. Enter nslookup

2.Type set type=MX and then press ENTER.

3. Enter domain. 

Or use the single line command:

nslookup -querytype=mx domain.com

nslookup examples

A. nslookup with no parameters
would return:
Your router's server and address.
D:\Users\akaplan>nslookup
Default Server:  isr-01.starhome.local
Address:  100.111.100.444

B. nslookup with server name as parameter
would return:
First section: Server and address of the server that provided you with the information.
Second section: domain name and IP address of the input server name.


D:\Users\akaplan>nslookup cms
Server:  isr-01.starhome.local
Address:  100.111.100.444

Name:    cms.starhome.local

Address:  100.223.333.127