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The Domain Name Service (DNS)

The Domain Name Service (DNS) A Protocol for resolving Domain Names to IP addresses and vice versa. (DNS can be used outside of the Internet framework also to resolve Names) A domain name example: Yahoo.com Because of the size of the Internet, and the large number of sites, it is

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The Domain Name Service (DNS)

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  1. The Domain Name Service (DNS) A Protocol for resolving Domain Names to IP addresses and vice versa. (DNS can be used outside of the Internet framework also to resolve Names) A domain name example: Yahoo.com Because of the size of the Internet, and the large number of sites, it is not feasible to store the correspondence between names and addresses in one location on one machine. Instead, the information is divided between many machines which are connected to each other and form a distributed system. Every user machine that requires Internet access must be configured with a local DNS address. This is the local node and is the first entry-point to the distributed DNS system. (Similar to the Default Gateway)

  2. A Domain is a subtree in the Domain name space. The name of a domain is determined by the name of the node at the top of the subtree. For example, the .com domain.

  3. The Domain Name Space A Domain is a sub-tree of the entire name Space Operates on the basis of a client-server relationship Generic sections: .org, .edu, .net etc Country Specific sections: .ie, .uk. .ca, .fr etc

  4. A Zone refers to the region of responsibility of a DNS server. If a domain is not split into smaller domains, then a zone and domain are equivalent. However if a DNS server delegates some of its authority to other servers, then a zone refers to the information kept by the second level servers.

  5. A recursive resolution of www.mcgraw.com when the client belongs to edu domain

  6. An iterative resolution of www.mcgraw.com from an edu client.

  7. DNS Cacheing To reduce the amount of searching for unavailable entries, and to speed up the resolution process, a DNS server that needs to consult other servers, will store the returned information in a local cache. The idea is that if the same name is to be resolved soon again, then the corresponding IP address is available. Information stored in the cache has a ‘Time to Live’ attached to it. This is attached by the ‘authoritative’ server which provided the resolution firstly. The mapping of name to IP address will not change within the TTL time. When a cached entry is older than the TTL value, it must be purged. DNS caching is vulnerable to attacks, where fake sites can masquerade as bona fide sites. (Poisoned caches)

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