Can you explain DNS
name resolution concept? Why I need to set DNS resolution for my Windows
or Linux server? How do I setup DNS name resolution under Linux / UNIX
server system?
A. DNS name resolution is nothing but resolving host names, such as www.nixcraft.com, to their corresponding IP addresses. DNS works as the "phone book" for the Internet by translating hostname into IP address or vise versa. Most DNS server stores following information:
a) Hostname and their IP address
b) List of mail server and their IP address for given domain name
c) Anti spam configuration and much more.
Without DNS name resolution, nothing will work on the Internet. Nobody likes to remember IP address, so DNS is foundation of many Internet services such as web, proxy, email and so on.
Each computer is configured to query specific name server. Usually home computers are configure to query ISP name servers or free dns name servers. Here is a typical UNIX / Linux /etc/resolv.conf file with nameserver IP address:
Sample output:
Each application can find www.yahoo.com IP address by sending a request to 208.67.222.222 or 208.67.220.220 IP address. This procedure is called hostname resolution and the algorithm that performs this operation is called the resolver. Let us see how to find out IP address for freebsd.nixcraft.in hostname:
A. DNS name resolution is nothing but resolving host names, such as www.nixcraft.com, to their corresponding IP addresses. DNS works as the "phone book" for the Internet by translating hostname into IP address or vise versa. Most DNS server stores following information:
a) Hostname and their IP address
b) List of mail server and their IP address for given domain name
c) Anti spam configuration and much more.
Without DNS name resolution, nothing will work on the Internet. Nobody likes to remember IP address, so DNS is foundation of many Internet services such as web, proxy, email and so on.
Resolving DNS names to IP addresses
When you type www.yahoo.com into a web browser, the application has to find out IP address associated with www.yahoo.com. Each part of network has DNS server or name servers. Each application send a request called dns lookup to DNS server. Each DNS server has limited information about host names and ip address. Almost all DNS server constantly query each other to get information using root servers.Each computer is configured to query specific name server. Usually home computers are configure to query ISP name servers or free dns name servers. Here is a typical UNIX / Linux /etc/resolv.conf file with nameserver IP address:
$ cat /etc/resolv.confSample output:
nameserver 208.67.222.222
nameserver 208.67.220.220Each application can find www.yahoo.com IP address by sending a request to 208.67.222.222 or 208.67.220.220 IP address. This procedure is called hostname resolution and the algorithm that performs this operation is called the resolver. Let us see how to find out IP address for freebsd.nixcraft.in hostname:
- The web browser will check local cache database to find out answer. If it can get an answer directly from these, it proceeds no further.
- Otherwise request will be sent to nameserver IP 208.67.222.222 to find IP address for freebsd.nixcraft.in host.
- 208.67.222.222 server will decide if that IP has been recently looked up before. If it has, there is no need to ask further, since the result would be stored in a local cache.
- 208.67.222.222 will see if the domain is local. I.e. if it is a computer that it has direct information about. In this case this would only be true if the 208.67.222.222 were Obsidian's very own name server.
- 208.67.222.222 will strip out the TLD (Top Level Domain) .in It will query a root name server, asking what name server is responsible for .IN. Depend upon the answer 208.67.222.222 will query authoritative server for IP address.
- 208.67.222.222 will return the result to the application.
- 208.67.222.222 will store each of these results in a local cache with an expiry date. To avoid having to look them up a second time.
