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DNS Name Server Functions, Name Server Architecture and General Operation
(Page 3 of 3)
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.
 Key Concept: The DNS name server hierarchy is logical in nature and not exactly the same as the DNS name server tree. One server may be responsible for many domains and subdomains. Also, the structure of the DNS name server hierarchy doesn’t necessarily indicate the physical locations of name servers.
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