DNS Server
Wednesday, August 6th, 2008
The Domain Name System (DNS) is a standard technology for managing the names of Web sites and other Internet domains. DNS technology allows you to type names into your Web browser like compnetworking.about.com and your computer to automatically find that address on the Internet. A key element of the DNS is a worldwide collection of DNS servers.
A DNS server is any computer registered to join the Domain Name System. A DNS server runs special-purpose networking software, features a public IP address, and contains a database of network names and addresses for other Internet hosts.
DNS Root Servers
DNS servers communicate with each other using private network protocols. All DNS servers are organized in a hierarchy. At the top level of the hierarchy, so-called root servers store the complete database of Internet domain names and their corresponding IP addresses. The Internet employs 13 root servers that have become somewhat famous for their special role. Maintained by various independent agencies, the servers are aptly named A, B, C and so on up to M. Ten of these servers reside in the United States, one in Japan, one in London, UK and one in Stockholm, Sweden.
DNS Server Hierarchy
The DNS is a distributed system, meaning that only the 13 root servers contain the complete database of domain names and IP addresses. All other DNS servers are installed at lower levels of the hierarchy and maintain only certain pieces of the overall database.
Most lower level DNS servers are owned by businesses or Internet Service Providers (ISPs). For example, Google maintains various DNS servers around the world that manage the google.com, google.co.uk, and other domains. Your ISP also maintains DNS servers as part of your Internet connection setup.
DNS networking is based on the client / server architecture. Your Web browser functions as a DNS client (also called DNS resolver) and issues requests to your Internet provider’s DNS servers when navigating between Web sites.
When a DNS server receives a request not in its database (such as a geographically far away or rarely visited Web site), it temporarily transforms from a server to a DNS client. The server automatically passes that request to another DNS server or up to the next higher level in the DNS hierarchy as needed. Eventually the request arrives at a server that has the matching name and IP address in its database (all the way to the root level if necessary), and the response flows back through the chain of DNS servers to your client.
Question: What is the difference between a router and hub or switch?
Answer: A router is a more sophisticated network device than either a switch or a hub. Like hubs and switches, network routers are typically small, box-like pieces of equipment that multiple computers can connect to. Each features a number of “ports” the front or back that provide the connection points for these computers, a connection for electric power, and a number of LED lights to display device status. While routers, hubs and switches all share similar physical appearance, routers differ substantially in their inner workings.
Traditional routers are designed to join multiple area networks (LANs and WANs). On the Internet or on a large corporate network, for example, routers serve as intermediate destinations for network traffic. These routers receive TCP/IP packets, look inside each packet to identify the source and target IP addresses and then forward these packets as needed to ensure the data reaches its final destination.
Routers for home networks (often called broadband routers) also can join multiple networks. These routers are designed specifically to join the home (LAN) to the Internet (WAN) for the purpose of Internet connection sharing. In contrast, neither hubs nor switches are capable of joining multiple networks or sharing an Internet connection. A home network with only hubs and switches must designate one computer as the gateway to the Internet, and that device must possess two network adapters for sharing, one for the home LAN and one for the Internet WAN. With a router, all home computers connect to the router equally, and it performs the equivalent gateway functions.
Additionally, broadband routers contain several features beyond those of traditional routers. Broadband routers provide DHCP server and proxy support, for example. Most of these routers also offer integrated firewalls. Finally, wired Ethernet broadband routers typically incorporate a built-in Ethernet switch. These routers allow several hubs or switches to be connected to them, as a means to expand the local network to accommodate more Ethernet devices.