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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  Name Systems and TCP/IP Name Registration and Name Resolution            9  TCP/IP Name Systems: Host Tables and Domain Name System (DNS)                 9  TCP/IP Domain Name System (DNS)                      9  DNS Name Servers and Name Resolution                           9  DNS Name Server Concepts and Operation

DNS Name Server Concepts and Operation 1 2 3 DNS Name Server Data Storage: Resource Records and Classes

The DNS Name Server Hierarchy is Logical, Not Physical

Like the other hierarchies, the name server hierarchy is logical in nature. I already mentioned that it often is not exactly the same as the authority hierarchy. For one thing, it is common for a single DNS name server to be the authoritative server for a number of domains. Even if a particular group has authority for a subdomain of a particular domain, it's possible they will “share” the DNS servers with the authority of their parent domain for efficiency reasons. For example, a university might delegate control over parts of its domain space to different groups (as in our example in the topic on DNS zones) but still manage all subdomains on the same server. In practice, the lower the level the subdomain in the DNS name hierarchy, the less likely that subdomain has its own DNS server.

Another important aspect of the logical nature of the name server hierarchy is that there is no necessary relationship between the structure of the name servers and their location. In fact, in many cases name servers are specifically put in different places for reliability reasons. The best example of this is the set of root name servers—despite all being at the “top” of the DNS server architecture, they are spread around the globe to prevent a single problem from taking all of them out. Also remember not to be fooled by the structure of a name in the geopolitical DNS name hierarchy—a name server called “ns1.blahblah.ca” might be in Canada, but it very well might not.

DNS Name Server Concepts and Operation 1 2 3 DNS Name Server Data Storage: Resource Records and Classes