A Network Administrator command  which help diagnosis DNS related issue. However to understand this,  you should better to know how DNS works.

How to troubleshoot DNS related issue.

1. NSLOOKUP example display "A Record" (IP Adress) of the domain




C:\Users\jpudasaini>nslookup jpudasaini.com.np 8.8.8.8
Server:  google-public-dns-a.google.com
Address:  8.8.8.8

Non-authoritative answer:
Name:    jpudasaini.com.np
Address:  216.239.32.21

A Non-Authoritative Answer is a response from Cache. A DNS server is
authoritative for zones actually holds it.

The above output shows "A Records" (IP Adress) of the domain
"jpudasaini.com.np". Which is actually query to the public Google DNS. If
you don't put DNS after the domain, it will used your default DNS, in my
case I have used public DNS.

2. MX Record using -query=mx

MX (Mail Exchange) record maps for the specific domain name to verify mail
exchaing servers on that domain.


C:\Users\jpudasaini>nslookup -query=mx gmail.com 8.8.8.8
Server:  google-public-dns-a.google.com
Address:  8.8.8.8

Non-authoritative answer:
gmail.com       MX preference = 40, mail exchanger =alt4.gmail-smtp-in.l.google
.com
gmail.com       MX preference = 20, mail exchanger =alt2.gmail-smtp-in.l.google
.com
gmail.com       MX preference = 10, mail exchanger =alt1.gmail-smtp-in.l.google
.com
gmail.com       MX preference = 30, mail exchanger =alt3.gmail-smtp-in.l.google
.com
gmail.com       MX preference = 5, mail exchanger =gmail-smtp-in.l.google.com

From the above example we can say that  4 MX records used for gmail
domain, the number associat with mx reference the preference of mail
server. Lower the number, higher the preference. So
gmail-smtp-in.l.google.com is the first server which received the mail at
first.

3. NS Record using -query=ns

NS (Name Server) records maps a domain to a list of DNS servers
authoritative for that domain. Here is example of name server which are
associated with jpudasaini.com.np doamain.

C:\Users\jpudasaini>nslookup -query=ns jpudasaini.com.np 8.8.8.8
Server:  google-public-dns-a.google.com
Address:  8.8.8.8

Non-authoritative answer:
jpudasaini.com.np       nameserver = ns4.afraid.org
jpudasaini.com.np       nameserver = ns2.afraid.org
jpudasaini.com.np       nameserver = ns1.afraid.org

4. SOA Record using -query=soa

 C:\Users\jpudasaini>nslookup -query=soa jpudasaini.com.np 8.8.8.8
Server:  google-public-dns-a.google.com
Address:  8.8.8.8

Non-authoritative answer:
jpudasaini.com.np
        primary name server = ns1.afraid.org
        responsible mail addr = dnsadmin.afraid.org
        serial  = 1511030001
        refresh = 86400 (1 day)
        retry   = 7200 (2 hours)
        expire  = 2419200 (28 days)
        default TTL = 3600 (1 hour)

SOA record (start of authority) which provides the authoritative
information, as well as e-mail address, serial no of the respective
domain.


5. Reserve DNS lookup

The reverse DNS look-up using IP Adress as argument to nslookup
C:\Users\jpudasaini>nslookup 216.239.32.21 8.8.8.8
Server:  google-public-dns-a.google.com
Address:  8.8.8.8

Name:    any-in-2015.1e100.net
Address:  216.239.32.21


6. Using Specific DNS Server

Make query using particular name server instead of using default DNS server.


C:\Users\jpudasaini>nslookup jpudasaini.com.np ns1.afraid.org
Server:  UnKnown
Address:  50.23.197.95

Name:    jpudasaini.com.np
Address:  216.239.32.21

On your outlook express while sending the emails and you get following error.

Cannot send the message. Verify the e-mail address in your account properties. The server responded: 550 Access denied - Invalid HELO name (See RFC2821 4.1.1.1)

1. Click Tools>Account
2. Select"View or change existing e-mail accounts" and click next
3. Select desire email account and click change
4. Click on "More Settings" at bottom of the page
5. Select on "Outgoing server" tab
6. Check "My outgoing server (SMTP) requires Authentication"
7. Select "use same settings as my incoming email server"
8. Click "Ok"
9. Press Next and Finished 

Step 1.
Free Download K9 web protection From here

Step 2. 
Choose "Get K9 Free for your Home" with your email address for free license.

Step 3.
 Install K9 web protection software. At the end it will ask for reboot, do it.

Step 4.
 After reboot open the "Blue coat K9 Web protection Admin"

Step 5.
Click Setup, it will ask for admin password, choose your admin password. (don't forget it, need it for future)

Step 6.
In my case I choose "Default" setting. This will block YouTube also. You can choose what you desire.

To open YouTube and block adult contain only, displaying by the site.

Step 7.
Go to other setting then choose "Advance YouTube Filtering"

How to send email through Telnet.

You can use it for troubleshoot purpose when sometime outgoing issue from the mail server.

1. First open the Command prompt. ctrl+r, now type "cmd".

before that you have to enable telnet service from control panel>program and feautre>Turn windows features on or off> now choose telnet client

2. Now, connect with telnet command just type

telnet mail.yourdomain.com 25



3. From the picture, you already enter into the server now use following command

helo mail.yourdomain.com



4. type mail from username, see on screenshots

mail from: username@yourdomain.com



5. Type receiver ID here, see screenshot.

rcpt to: yourfriend@hotmail.com, yourfriend@yahoo.com



6. To add message just use "data" command and type "subject" command. At the end don't forget to add "." to end the message and press enter.
data
subject: this is test email

hello,

This is jpudasaini.com.np, the portal where you can hangout for tutorial on the job training.

Regards
jpudasaini.com.np

.

7 Type quit to exit.

(change "domainname" with your desire domain.)

1. Open a DOS Command Prompt
2. Type "nslookup"
3. Your computer's DNS server name and IP address will be displayed.
4. Now just type "set type=mx" - this will force NSLOOKUP to shows Mail eXchange records from the DNS servers.
5. You can try using gmail.com or use your own domain name.
6. you can see below output.

Suddenly I encounter a weird problem with VMware 9 version. I install different OS for my education and testing purposed. Like MAC os, Ubuntu, CentOS, BT, WinXP, Win-server 2003. When I tried to run one of this OS a error message appear.



unable to open kernel device "\\.Global\vmx86": The system cannot find the file specified. Did you reboot after installing VMware Workstation?
Failed to initialize monitor device.

Click ok you can see this window

In my daily office tasks, I often need to measure the actual throughput of local network links, whether wired or wireless. To accomplish this, I use the iPerf tool, which is ideal for this purpose.

In this tutorial, I’ll guide you on how to use iPerf effectively. Since I’m demonstrating this on Windows, start by downloading iPerf for Windows and placing it on your Desktop or another location of your choice.

Now go to that folder using cd [FolderName], in my case I place it on desktop.


C:\Users\jpudasaini\Desktop\iperf>dir
Now its time to create the SERVER first, use following command to create a server,

C:\Users\jpudasaini\Desktop\iperf>iperf -s

As you can see  that you are in iperf directory, from just use following command to test the actual bandwidth of the link

C:\Users\jpudasaini\Desktop\iperf>iperf -c 10.10.10.10
If you like to test bidirectional use this command

C:\Users\jpudasaini\Desktop\iperf>iperf -c 10.10.10.10 -d

I encounter a problem installing WinPcap in windows 8 when I try to install GNS3. So I search and found the resolution for that. 

Make sure You download WinPcap. Go the folder and right click the WinPcap_x.x.exe file then go the properties, on properties window click on Capabilities tab, now check on "run this program in compatibility mode for:" choose windows 7 from drop down menu. See the picture below.