Understanding DNS setting

What is an MX Record

MX stands for Mail Exchange Records. MX records are used in DNS records(or Zone files) to specify how email should be routed.
Lets take an example of say liz@mydomain.com.
This is how a typical DNS record(for mydomain.com) looks like.

---

;

; Zone file for mydomain.com

@ 14400 IN SOA ns.mynameserver.com. root.ns.mynameserver.com. (

                       109157199 

                       86000 

                       7200 

                       3600000 

                       600 ) 

mydomain.com. 14400 IN NS ns.mynameserver.com. 

mydomain.com. 14400 IN NS ns2.mynameserver.com. 

mydomain.com. 14400 IN NS ns3.mynameserver.com.

; A Record

mydomain.com. 14400 IN A 216.34.94.184

localhost.mydomain.com. 14400 IN A 127.0.0.1

; MX record

mydomain.com. 14400 IN MX 0 mydomain.com. 

mail 14400 IN CNAME mydomain.com. 

www 14400 IN CNAME mydomain.com. 

ftp 14400 IN CNAME mydomain.com. 

---

Notice the line with the ``MX'' in it. This is called the MX record.

mydomain.com. 14400 IN MX 0 mydomain.com. 

The MX record shows that all emails @ mydomain.com should be routed to the mail server at mydomain.com. The DNS record shows that mydomain.com is located at 216.34.94.184. This means that email meant for liz@mydomain.com will be routed to the email server at 216.34.94.184. This finishes the task of the MX record. The email server on that server(say sendmail) then takes over, collects the email and then proceeds to distribute it to the user ``liz''.
It is important that there be a dot(``.'') after the domain name in the MX record. If the dot is absent, it routes to ``mydomain.com.mydomain.com''. The number 0, indicates Preferance number. Mail is always routed to the server which has the lowest Preferance number. If there is only one mail server, it is safe to mark it 0.

Multiple mail servers

Multiple email servers are useful for the sake of redundancy. If the Highest Priority email server (one with the lowest Preference number) is down, then the email is routed to the Server with the second highest Preference number.
For example

mydomain.com. 14400 IN A 216.34.94.184

server2.mydomain.com. 14400 IN A 216.34.94.185

mydomain.com. 14400 IN MX 0 mydomain.com. 

mydomain.com. 14400 IN MX 30 server2.mydomain.com. 

You can have unlimited MX entries for Fallback.
If all the MX records are equal Preference numbers, the client simply attempts all equal Preference servers in random order, and then goes to MX record with the next highest Preference number.

Pointing MX records to an IP

Its not possible to have an MX record pointing directly to an IP. For example 'mydomain.com. 14400 IN MX 0 216.34.94.184`` is wrong. Define an ``A Record'' first and then have the MX record pointing to it.

server2.mydomain.com. 14400 IN A 216.34.94.185

mydomain.com. 14400 IN MX 30 server2.mydomain.com. 

MX records for Subdomains

A Subdomain is something like this ``Subdomain.mydomain.com''. Assume you want to send an email to liz@subdomain.mydomain.com and to capture that on another server.

mydomain.com. 14400 IN A 216.34.94.184

server2.mydomain.com. 14400 IN A 216.34.94.185

mydomain.com. 14400 IN MX 30 mydomain.com. 

subdomain.mydomain.com. 14400 IN MX 30 server2.mydomain.com. 

In this configuration, liz@subdomain.mydomain.com would go to 216.34.94.185 and liz@mydomain.com would go to 216.34.94.184.

Testing the MX record

Once you setup your MX record, always test it to see if it is setup correctly. You can do with tools like nslookup.

---

[root@localhost sangeetha]# nslookup

> set q=mx 

> yahoo.com 

Server: 192.168.1.1 Address: 192.168.1.1#53

Non-authoritative answer: 

yahoo.com mail exchanger = 1 mx1.mail.yahoo.com. 

yahoo.com mail exchanger = 1 mx2.mail.yahoo.com. 

yahoo.com mail exchanger = 1 mx3.mail.yahoo.com. 

yahoo.com mail exchanger = 5 mx4.mail.yahoo.com.

Authoritative answers can be found from: 

yahoo.com nameserver = ns2.yahoo.com. 

yahoo.com nameserver = ns3.yahoo.com. 

yahoo.com nameserver = ns4.yahoo.com. 

yahoo.com nameserver = ns5.yahoo.com. 

yahoo.com nameserver = ns1.yahoo.com. 

mx1.mail.yahoo.com internet address = 4.79.181.14 

mx1.mail.yahoo.com internet address = 4.79.181.15 

mx1.mail.yahoo.com internet address = 67.28.113.10 

mx1.mail.yahoo.com internet address = 67.28.113.11 

ns1.yahoo.com internet address = 66.218.71.63 

ns2.yahoo.com internet address = 66.163.169.170 

ns3.yahoo.com internet address = 217.12.4.104 

ns4.yahoo.com internet address = 63.250.206.138 

ns5.yahoo.com internet address = 216.109.116.17 

Callback connection setting

The callback feature instructs your remote access server to disconnect, and then to call you back, after you dial in.

What does it mean and what for ?
Call the server from your home, then immediately hanging up by the server and then server dialing you back.
Required callback enhances network security by ensuring that only users from specific locations can access the server. By dropping the call, and then calling back a moment later to the preassigned callback number, most impersonators can be thwarted.

How it work ?



You call the server to the server via modem, once your server modem response, your connection automatically disconnected then your server call you back.

What for ?
For example, you need some file from your network server while you are at home or you are out of office, and this is reduce your phone charge and the others one, you can used internet trough your server network as a gateway.

How to Setting ?

Office/Server Setting:
step 1: Incoming Connection

Open Network Connection -> Create a new connection -> Next -> Select Set up an Advance Connection -> Next -> Accept incoming connection -> Select your modem device -> Do not allow virtual private connection -> select User Permission -> Next -> Finish.

step 2:
Set Remote Access Server (RAS)
Of course this part must configured by your administrator (if you want to know how to configure RAS, ask me). If you are as a user, put the modem to your computer as your network client, then do the only step1, and of course you have to let your computer on when you leave.

Your Home Computer setting:
step 1:

Open Network Connection -> Create a new connection -> Next -> Connect to the Internet -> Next -> Setup my connection manually -> Connect using a dial-up modem -> Type connection name -> Next -> Type the Phone Number -> Type User Name and password that you has been permission to connect as above (server configuration) -> Next -> Finish.

step 2:
Open Network Connections.
On the Advanced menu, click Dial-up Preferences.
On the Callback tab, do one of the following:
1. If you do not want to use callback, click No callback.

2. If you want to decide whether to use callback at the time you connect, click Ask me during dialing when the server offers.

3.If you want to use callback consistently, click Always call me back at the number(s) below, and select the modem or device on which you want to be called back.

4.If Phone number is blank for the device you have selected, click Edit, and then type the number.

5.If you want to remove a modem or device from the list of possible callback devices, click the modem or device, and then click Delete.

(see the final setting screen)


Now try connect to your computer office.
The surprised is,
1. The phone cost become to your office computer phone line. Your cost only on the first called.
2. If your office computer able to connect the internet via you server connection, you can used internet too from your home (must check your office computer firewall setting).

SMTP Investigation for Telkom adsl connection

Investigate SMTP Connection for TELKOM ADSL :

Below is a FAQ to investigate SMTP Relay, smtp.telkom.net. Follow this step to do smtp investigation:

1. Run test nslookup to the smtp telkom server :

IP not found from smtp.telkom.net?, check your DNS number, don’t know your DNS number ? You can asked what’s the DNS number for your telkom connection to astinet customer service (147).

2. Run ping to smtp server :



When your ping results is RTO (Request Time Out), that’s means your computer/network is unconnected with telkom server. You have to checked your adsl connection or adsl modem indicator. ADSL indicator lamps is blink that’s mean no adsl signal to your modem or cannot login.

3. Tracert into smtp server :


Tracert result display is indicated server found.


4. Test send email via telnet :



Sending email via telnet, used for tested into smtp telkom.net server. Do this test if sending mail via Outlook express failed.

Above picture is a Linux testing result, for the process step you can do via cmd (command prompt) windows, but the words that you type is disappear.

If you see the above picture result, that’s means sending email via telnet is successful, but send mail using Outlook Express almost failed, Had to checked your Outlook express software.

If all step had been done, but cannot send mail, check from your server side :

1. Are your server using Firewall ?
2. Check your ADSL configuration, do not block smtp (25 port)
3. Do you have anothers application problem with your server ?, example : wingate ?

Note for wingate had special configuration for SMTP mail server, check your wingate configuration.


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