1-The DNS domain namespace, as shown in the following
figure, is based on the concept of a tree of named domains.
Each level of the tree can represent either a branch or a
leaf of the tree. A branch is a level where more than one
name is used to identify a collection of named resources. A
leaf represents a single name used once at that level to
indicate a specific resource.
DNS Domain namespace
The previous figure shows how Microsoft is assigned
authority by the Internet root servers for its own part of
the DNS domain namespace tree on the Internet. DNS clients
and servers use queries as the fundamental method of
resolving names in the tree to specific types of resource
information. This information is provided by DNS servers in
query responses to DNS clients, who then extract the
information and pass it to a requesting program for
resolving the queried name.
In the process of resolving a name, keep in mind that DNS
servers often function as DNS clients, querying other
servers in order to fully resolve a queried name. For more
information, see How DNS query works.
The creation of host tables to map computer names to
addresses greatly improved the usability of the early
Internet and the TCP/IP protocol suite that implemented it.
Unfortunately, while the host table name system worked well
when the internetwork was small, it did not scale
particularly well as the Internet started to grow in size
and complexity. The name system had to stay but the use of
host tables had to be dispensed with in favor of a newer,
more capable system.
Over the period of several years, many engineers worked to
create a system that would meet not just the needs of TCP/IP
internetworks of the time, but also of the future. The new
name system was based on a hierarchical division of the
network into groups and subgroups, with names reflecting
this structure. It was designed to store data in a
distributed fashion to facilitate decentralized control and
efficient operation, and included flexible and extensible
mechanisms for name registration and resolution. This new
name system for TCP/IP was called the Domain Name System (DNS).
In this section I describe the concepts behind TCP's Domain
Name System, as well as its operation. The section is
divided into four subsections. The first provides and
overview of DNS, including a description of its
characteristics and components. The next three subsections
describe how DNS implements each of the three primary name
system functions: the DNS name space and architecture; the
DNS name registration process, including hierarchical
authorities and administration; and the DNS name resolution
process, focusing on how name servers and resolvers work.
Finally, I have a topic that briefly highlights the changes
made to DNS to support the new version 6 of the Internet
Protocol, and its much longer addresses.
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Other Programming Languages AllOther Interview Questions
How many processes can listen on a single TCP/IP port?
1. What is the effect of the OPTIONS statement ERRORS=1?
2. What’s the difference between VAR A1 - A4 and VAR A1 — A4?
3. What do the SAS log messages "numeric values have been
converted to character" mean?
4. What are the implications?
5. Why is a STOP statement needed for the POINT= option on a
6. How do you control the number of observations and/or
variables read or written?
Approximately what date is represented by the SAS date value
7. How would you remove a format that has been permanently
associated with a variable??
8. What does the RUN statement do?
9. Why is SAS considered self-documenting?
10. What areas of SAS are you most interested in?
11. Briefly describe 5 ways to do a "table lookup" in SAS.
12. What versions of SAS have you used (on which platforms)?
13. What are some good SAS programming practices for
processing very large data sets?
14. What are some problems you might encounter in processing
missing values? In Data steps? Arithmetic? Comparisons?
Functions? Classifying data?
15. How would you create a data set with 1 observation and
30 variables from a data set with 30 observations and 1
16. What is the different between functions and PROCs that
calculate the same simple descriptive statistics?
17. If you were told to create many records from one record,
show how you would do this using arrays and with PROC
18. What are _numeric_ and _character_ and what do they do?
19. How would you create multiple observations from a single
20. For what purpose would you use the RETAIN statement?
21. What is a method for assigning first.VAR and last.VAR to
the BY group variable on unsorted data?
22. What is the order of application for output data set
options, input data set options and SAS statements?
23. What is the order of evaluation of the comparison
operators: + - * / ** ( ) ?
24. How could you generate test data with no input data?
25. How do you debug and test your SAS programs?
26. What can you learn from the SAS log when debugging?
27. What is the purpose of _error_?
28. How can you put a "trace" in your program?
29. Are you sensitive to code walk-throughs, peer review, or
30. Have you ever used the SAS Debugger?
31. What other SAS features do you use for error trapping
and data validation?
32. How does SAS handle missing values in: assignment
statements, functions, a merge, an update, sort order,
33. How many missing values are available? When might you
34. How do you test for missing values?
35. How are numeric and character missing values represented
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37. How to do user inputs and command line arguments in SAS?
38. How to convert a given date value into SAS date
39. How do i read multiple spaces in datasets?