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module19-dnsv2

module19-dnsv2 - DNS Domain Name System Domain names and IP...

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DNS Domain Name System
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Domain names and IP addresses People prefer to use easy-to-remember names instead of IP addresses Domain names are alphanumeric names for IP addresses e.g., neon.cs.virginia.edu, www.google.com, ietf.org The domain name system (DNS) is an Internet-wide distributed database that translates betweem domain names and IP addresses How important is DNS? Imagine what happens when the local DNS server is down.
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Before there was DNS …. …. there was the HOSTS.TXT file Before DNS (until 1985), the name-to-IP address was done by downloading a single file (hosts.txt) from a central server with FTP. Names in hosts.txt are not structured. The hosts.txt file still works on most operating systems. It can be used to define local names.
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Resolver and name server 1. An application program on a host accesses the domain system through a DNS client, called the resolver 2. Resolver contacts DNS server, called name server 3. DNS server returns IP address to resolver which passes the IP address to application Reverse lookups are also possible, i.e., find the hostname given an IP address HTTP Resolver Hostname (neon.tcpip-lab.edu) IP address (128.143.71.21) Name server Hostname (neon.tcpip-lab.edu) IP address (128.143.71.21)
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Design principle of DNS The naming system on which DNS is based is a hierarchical and logical tree structure called the domain namespace . An organization obtains authority for parts of the name space, and can add additional layers of the hierarchy Names of hosts can be assigned without regard of location on a link layer network, IP network or autonomous system In practice, allocation of the domain names generally follows the allocation of IP address, e.g., All hosts with network prefix 128.143/16 have domain name suffix virginia.edu All hosts on network 128.143.136/24 are in the Computer Science Department of the University of Virginia
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Managed by UVA DNS Name hierarchy DNS hierarchy can be represented by a tree Below top-level domain, administration of name space is delegated to organizations Each organization can delegate further Managed by CS Dept. . (root) com virginia.edu gov edu org uci.edu cs.virginia.edu math.virginia.edu neon.cs.virginia.edu Top-level Domains
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Domain name system Each node in the DNS tree represents a DNS name Each branch below a node is a DNS domain .
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