Learn about Domain Name System (DNS)

Updated 4/10/2017 12:36:38 PM by Comcast Expert


This will provide an overview of Domain Name System (DNS).

Comcast Domain Name System (DNS) servers:

  • Primary IPv4:

  • Secondary IPv4:

  • Primary IPv6:  2001:558:FEED::1

  • Secondary IPv6:  2001:558:FEED::2

Please see the following Help & Support articles for more information on how and where to apply these settings:

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Common Terms

Host names are labels assigned to devices connected to a computer network used to identify the device.  World Wide Web (www) is to most common host name.

Domain names are easily remembered names used to represent IP addresses on the internet.

  • Alphanumeric equivalent of an IP address

  • Easier to remember "comcast.com" than an IP address

Uniform Resource Locater (URL) is another term for a web address.

What is DNS?

DNS is a naming system for computers, services, or any other resource connected to the internet or a private network. Its function is to translate domain names to IP addresses for the purpose of locating computers and services worldwide.

DNS is like a phone number for a website. In a phonebook, John Doe is associated with phone number 215-555-5555. On the Internet, the domain name www.comcast.com would be associated with an IP address of In this example, "www" is the host name and comcast.com is the domain name.

How does DNS work?

When a user types www.comcast.com into a browser, that browsers sends a query to a recursive server. That recursive server sends a query to the Root server, which responds with a referral to the Top Level Domain (TLD) server, in this case, the TLD servers for .COM. The TLD server will respond with a referral to the zone owner (in this case comcast.com), and that zone owner's server will respond with the IP address of the web server for www.comcast.com.

Reverse DNS

Reverse DNS uses the same process as DNS when a user knows the IP address of the resource he or she wishes to reach. The user types the IP address into the browser and the same process used when typing the URL in would be followed to get the user to the correct resource or website.

Record Types used with DNS

There are various types of records used in DNS the most commonly used include SOA, NS, A, MX, CNAME and PTR records

Start of Authority (SOA) records

The SOA Record identifies the organization in charge of managing DNS records for a zone.

  • The authoritative name server contains the zone where DNS queries are sent.

  • The customer sets the SOA by assigning DNS servers with their registrar.

  • Comcast is not required to be the SOA in order for customers to have Web Hosting or Email services with Comcast.

  • Any company can perform DNS hosting while Comcast or other companies host Email and/or Web services.

NS records

NS or Name Server records state the primary and backup name servers for the respective domain. There must be at least 2 NS records in each zone.

A records

Address records (A records) translate a domain name into an IP address.

IPv6 AAAA record

IPv6 Address Records (AAAA Records) translate a domain name into an IPv6 address.

MX records

MX or Mail Exchange records specify where the mail should be delivered for the domain.

MX records allow mail to be delivered to the correct E-mail Server. In order for e-mail to be functioning properly on a domain, there must be at least 1 MX record.

It is common to have a backup Mail Server and a corresponding MX record.

CNAME records

A Canonical Name (CNAME) record is a type of resource record in the DNS that specifies that the domain name is an alias of another CNAME. Canonical, in the case of DNS, means a more generally accepted or standard name.

PTR records

Pointer (PTR) records map an IP address to a canonical name. Its primary use is reverse DNS lookup. Reverse DNS is commonly used to associate the IP address of a sending mail server to the domain that the server uses to identify itself. Many receiving mail servers will first confirm that the IP address of the server sending it mail has a PTR record that refers to the domain name that the sending server is using. Often, recipient mail servers will reject the email if the sending server does not have a valid PTR. Not all receiving servers perform this check. All changes to PTR records must be done by the owner of the IP space. Comcast only has authority to modify the PTR records of IP addresses that it leases.

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