What is dns exactly ?

Written by Swapnil on October 1, 2008 – 11:47 am -

What is a nameserver?

A nameserver is the program that actually does the work of looking up names. There are three main types of nameserver. A CACHING-ONLY nameserver does look-ups of names, but controls no name records itself. A PRIMARY nameserver not only does lookups of names, but also owns the records for a domain. A SECONDARY nameserver does name lookups, and it also backs up a primary nameserver by providing authoritative answers for a certain domain. Many nameservers will combine Primary and Secondary functionality for different domains.

What is Primary vs Secondary DNS?

The domain name space is divided into regions called zones. In order to maximize availability, the InterNIC (Internet’s Network Information Center) requires that every zone have both a primary and secondary DNS server.

Everybody maintain two public nameservers, ns1 and ns2. When used for primary DNS, ns1 acts as the primary and ns2 as a secondary. You only need to submit a single request for primary DNS service to enable ns1 as your primary and ns2 as your secondary.

When used for secondary DNS, all of name servers act as secondary nameservers that obtain data by way of zone transfers from the primary of your choice. You only need to submit a single request for secondary DNS service to enable our name servers as secondary name servers for your zone.

What is an MX record?

When a remote site on the internet wants to send someone at your domain an e-mail message, their mail server software looks up the hostname of the appropriate mail server to receive that mail. This type of record is referred to as an “MX,” “Mail Exchanger” or “Mail Relay” record. The response that the remote server gets tells it where to send the mail so that it will be relayed to you. When your site has received e-mail it is stored for you by your e-mail server. In order to retrieve your mail from the server you need to use an interface between your mail program and the mail server itself. This interface is usually a piece of software like POP (the Post Office Protocol) or IMAP. The hostname that you use to access the POP or IMAP server might be the same as your MX record, or it might be different. MX records are used to direct mail to specific locations. For example, if you had two hosts that work as mailhosts, you could identify them with MX records. More often, you create an MX record to tell others outside your domain (i.e. on the Internet) how to get mail to you.

The difference between forward (A) and reverse (PTR) records.

Forward records, or A records, are those which translate from machine names to ip addresses. These are the most commonly used records. A typical A record is constructed as follows:

eukhost.test.com. IN A 192.168.1.1

(this example shows an A record which correlates the machine name eukhost.test.com to the IP address 192.168.1.1)

Reverse records, or PTR records, are those which translate from ip address to machine names. They are typically used for security tests. The IP address of a machine is reversed, and then the suffix in-addr.arpa is appended. A typical PTR record is:

1.168.1.192.in-addr.arpa. IN PTR eukhost.test.com.

(this example shows a PTR record which correlates the IP address 192.168.1.1 to the machine name eukhost.test.com)

The DNS “Time To Live” (TTL)

Each part of DNS information that may be cached separately has a time to live associated with it. Once this time expires, the cached information must be discarded and has to be obtained from an authoritative server again if it is needed. The TTL is not configured locally in the caching server but is set in the authoritative server and passed along with the information itself. This way the administrator of a domain can control how long it takes for any change to be known throughout the Internet.

What/Who is ICANN?

ICANN, which is short for the Internet Corporation for Assigned Names and Numbers, is a central authority in an essentially decentralized, neutral and ungoverned global network of networks. Icann runs the addressing system, giving out blocks of unique identifiers to countries and private registries.
ICANN was created through a Memorandum of Understanding (MoU) between the U.S. Department of Commerce and ICANN to transition management of the Domain Name System (DNS) from the U.S. government to the global community.
The Internet Corporation for Assigned Names and Numbers is responsible for managing and coordinating the Domain Name System (DNS) to ensure that every address is unique and that all users of the Internet can find all valid addresses. It does this by overseeing the distribution of unique IP addresses and domain names. It also ensures that each domain name maps to the correct IP address.
ICANN is also responsible for accrediting the domain name registrars. “Accredit” means to identify and set minimum standards for the performance of registration functions, to recognize persons or entities meeting those standards, and to enter into an accreditation agreement that sets forth the rules and procedures applicable to the provision of Registrar Services.

What is Dynamic DNS?

Dynamic DNS allows machines with IP addresses that change to have permanent addresses on the internet. You can buy a domain name anywhere, and then point that domain name to your machine. Before dynamic DNS you had to have a fixed IP to run a web server. Now you can run a web server with a cable modem, DSL line or even on a dial up.

What is a CNAME? (Canonical Name Records)

CNAME records simply allow a machine to be known by more than one hostname. There must always be an A record for the machine before aliases can be added. The host name of a machine that is stated in an A record is called the canonical, or official name of the machine. Other records should point to the canonical name. Here is an example of a CNAME:

www.eukhost. IN CNAME scott.eukhost.com.

You can see the similarities to the previous record. Records always read from left to right, with the subject to be queried about on the left and the answer to the query on the right. A machine can have an unlimited number of CNAME aliases. A new record must be entered for each alias.

What are Start of authority (SOA) records?

The SOA record is the most crucial record in a DNS entry. It conveys more information than all the other records combined. This record is called the start of authority because it denotes the DNS entry as the official source of information for its domain.

Other records

There are many other types of DNS records, like Host Information (HINFO) or Text (TXT) are informational for people only, listing facts about the domain and types of computers used that are not vital to the operation of DNS.

What is propagation?

Propagation is the time it takes all DNS servers and Internet Service Providers to update their DNS tables to reflect any new website locations. The rate at which this happens can vary among providers. New domain name registrations are usually live on the main root servers within 24 hours of registration completion. You may need to allow additional time for this information to trickle down to all the DNS Servers on the Internet. Transfers will take approximately 72 hours to be live in the root servers.

During propagation, your website may be viewable from one ISP, and not another. We suggest you wait 72 hours before announcing your new domain name to the world.

What is IP pointing?

IP Pointing allows you to forward your domain traffic to a specific IP address. A server is required at the designated address to use this forwarding method.

What is a lame delegation or lame response? How do I fix it?

You may see in your name server logs a message about a lame response or lame delegation. When performing recursion, the process of looking up a record from the DNS, a name server must generally query several servers, follow up on referrals, and go down the chain of authority to find the answer.
For each query, the recursing name server expects the other name server to be authoritative for a given zone. For example, the root servers are expected to be authoritative for the root zone. The root servers give out a referral for com, pointing to a set of servers; any such server is expected to be authoritative for com. The expected authority can be obtained either from a referral for that zone from a parent zone, or from the authority records returned by another authoritative name server for the zone.
If a query is answered in a way that indicates that the responder is not authoritative for the expected zone, the result is called lame. Since the response is almost always in the form of a referral (a delegation response) for either some zone higher up on the tree or for the expected zone itself, the response can be called a lame delegation or lame referral.

A perfect DNS guide…


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Configure Virtual Private Network on Windows Virtual Private Server.

Written by Pritam on September 22, 2008 – 6:02 am -

Following steps to configure the Virtual Private Network on Windows Virtual Private Server.

1. For windows Virtual Private Server, First you need to enable “NAT” for your Virtual Private Server. This must be done from the Main Hardware Node. We will do it on our Main Hardware Node.

2. After enabling “NAT” for your Virtual Private Server, Go to Start >> RUN >> Type “services.msc” in you Virtual Private Server
On the services list, select “Routing and Remote Access” and go to properties. Make the startup type automatic and apply. After that you should have the option to “Start” this service. Start this service as we are going to use this service basically to route our traffic

3. Now go to Start >> Settings >> Control Panel >> Administrative Tools >> Click on the shortcut says “Routing and Remote Access”. It should open the configuration panel of Routing and Remote Access.

4. Now right click on your computer name the click the option says “Configure and Enable remote and routing access”. Before doing this, make sure your Firewall service is stopped and disabled.

5. Now on the configuration wizard click Next to proceed >> In the configuration list select “Custom Configuration”, Press Next >> Select Virtual Private Network Access & NAT and Basic Firewall Option, Press Next >> Now press Finish to end the wizard.

This wizard should enable the PPTP & L2TP Virtual Private Network access to your firewall with private routing capability. Now you need to configure your Virtual Private Server to route the private Traffic to the Public Interface. To do this, we need to have any of the following two:

1. Two network interface to route one to another. or
2. We can use NAT (Network Address Translation) using the Microsoft Loopback adapter.

We will basically work with the 2nd one as Virtual Private Server don’t come with two network interfaces. To continue with the NAT configuration, go to the Routing and Remote Access panel >> Expand ComputerName (Local) >> Expand Ip Routing >> You should find a option says “NAT/Basic Firewall”. Simply right click on that option and use the New interface to add network translation. Now first add the Inferface says “Internal” which is basically for private network access with default settings and on second attempt add your main adapter to the NAT list and select the options says “Public Interface connected to this inferface” and select the option says “Enable NAT on this interface”.

Now your network should have the address translation working, that means your private requests should be now translated and you can use this Virtual Private Network as your internet gateway.

Now to allow your users to use Virtual Private Network, add a new user and from the properties allow its Dial In permission. User with Dial-In permission should be able to login using Virtual Private Network.


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