DNS - BACK to Basics

The Domain Name System (DNS) helps identify all resources on the Internet.

To begin, we will cover the fundamentals of DNS.

The most important role of DNS for the majority of us is translating names into IP addresses so that network communications can occur.

Common DNS Records used by CipherWave

Types of DNS Records.

MX Record (Domain Example: Cipherwave.co.za)

MX stands for “mail exchanger”.


What happens when someone sends an email to an @cipherwave.co.za email address ?

The sending mail server will look up the MX records in DNS by following a sequence along these lines:

  1. Look up the authoritative name servers for Cipherwave.co.za
  2. Query the Cipherwave.co.za name servers for the MX records
  3. Look up the names of the MX records in DNS to get their IP addresses


If you were to run your own manual DNS lookup of the MX records for CipherWave.co.za it would look something like this:


Open CMD.exe

Type nslookup and press "Enter"

Type server 8.8.8.8 and Pres "Enter"

Type set q=mx and Press "Enter"

Type Cipherwave.co.za and Press "Enter"


The Results should be 

on-authoritative answer:cipherwave.co.za        MX preference = 10, mail exchanger = mx02.ciphercloud.co.zacipherwave.co.za        MX preference = 5, mail exchanger = mx01.ciphercloud.co.za


MX Preferences

You may notice the “MX preference” in the output above and wonder what that is referring to.


Notice that there are multiple MX records each with a different preference value. The preference is basically a way of setting the priority of each MX record. The lowest preference is the MX with the highest priority, ie the one that a sending mail server should try first.

The purpose of multiple MX records is to either:

  • Provide some load balancing by using multiple MX records with the same preference set
  • Provide a backup MX that can be used if the primary one is unavailable

The backup MX may be another mail server in your organization at a secondary site that has less bandwidth available to it. Or it could be a server hosted by a third party that provides backup MX services. Either way the purpose is to give sending email systems somewhere to send messages rather than have to store them and retry later.


CNAME Record (Domain Example: CipherWave.co.za)


CNAME stands for Canonical Name. 

CNAME records can be used to translate one dns record to another.


For example, if you have a server where you keep all of your documents online, it might normally be accessed through docs.cipherwave.co.za. You may also want to access it through documents.cipherwave.co.za. One way to make this possible is to add a CNAME record that points documents.cipherwave.co.za to docs.cipherwave.co.za

When someone visits documents.cipherwave.co.za, they will see the exact same content as docs.cipherwave.co.za.

An example is shown below.

documents                 IN      CNAME             docs.cipherwave.co.za.

(The full stop at the end of the record is important, as highlighted above.)


A Records (Example Domain: CipherWave.co.za)

A Records are the most basic type of DNS record and are used to point a domain or subdomain to an IP address.

Test                 IN      A             41.87.205.2

When someone visits Test.cipherwave.co.za it will forward the request to 41.87.205.2.


SPF & TXT Records (Example Domain: CipherWave.co.za)


A TXT record is used to store any text-based information that can be grabbed when necessary. We most commonly see TXT records used to hold SPF data and verify domain ownership


cipherwave.co.za.               IN      TXT     "v=spf1 a:pinpoint-ah-omx4.synaq.com"


The above record is an example of an TXT record used to authorize pinpoint-ah-omx4.synaq.com to send email on behalf of the CipherWave.co.za domain.


Test

DNS Record Test

You need to create a DNS record for a customer that points ftp.ciphervault.co.za to 41.56.2.3

Please enter the DNS record below.

   IN         

 

You need to create a DNS record for a customer that points ftp.ciphervault.co.za to www.cipherwave.co.za

Please enter the DNS record below.

 

 IN