The Function of Domain Name Service

by Mike on November 7, 2008 · 1 comment

in DNS Server

DNS Service
DNS manages the mappings between host names, like or, to Internet addresses. The host names exist because it is easier for humans to remember the host name rather than the number.
Every host name must have a registered DNS server so that the resolving of hosts to IP numbers can occur. In fact, DNS is used by all of the networking processes and programs including web browsers and FTP. A Forward LookUp goes from domain name to IP Address and a Reverse LookUp goes form IP Address to domain name.
DNS is managed in zones. When you run a DNS server you are managing your zone. This means that manages the zone. The information about your site is in that zone which is made available by your DNS server to other zones across the Internet. Your DNS server accesses the information in other zones across the Internet for information as it is needed.
DNS Client
Every machine that will access the Internet must configure their system to access a local DNS server. The local DNS server provides information about domain names to the the client. For example, if a client is trying to send an email to the client DNS resolver will make a request to the local DNS server which they have configured on their system as the first DNS server. When the local DNS server is contacted it will access the DNS cache that it maintains to see if it knows the IP Address and authoritative server for If it knows it sends this information to the client that made the request. If the local DNS server does not know it will contact a Root DNS server which will provide the information to the local DNS server and then the local DNS server sends the information to the client. Once the client is provided this information the email is sent to the correct mail server at In the example, you see how very important DNS is to the whole process of mail servers.
The /etc/resolv.conf file contains a list of the domain servers that the client will look to for DNS.
cat /etc/resolv.conf
The client will typically make the request using port number 53 UDP to the first nameserver listed in the /etc/resolv.conf. If the first nameserver does not respond the second one listed will be contacted.

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ip addresses December 14, 2008 at 3:13 pm

Large numbers of infected computers have been searching in vain for the Srizbi botnet disrupted by the disconnection of ISP McColo a week ago, a security vendor has found. According to FireEye Security, the company has detected a total of

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