Tutorial #9
- In the RR examples given in the lecture, the TTL field is set to 86400.
What is the significance of this strange number?
- The DNS is described as a "distributed database" of RRs.
- What does this mean?
- What is the alternative, and why is it generally regarded as unworkable?
(Optional philosophical discussion question: How does this
second alternative compare (conceptually) with the various Web "search
engines" such as Google and AltaVista?)
- A nameserver acts not only as a server, but also as a client under certain
circumstances. What are these circumstances?
- Why[1]
should each nameserver know the IP address of its parent instead of its domain
name? Similarly -- when configuring an Internet-connected computer, why is the
nameserver always specified as an IP address, not as a domain name?
- Nameservers are usually (always?) configured to know the IP address of at
least one root nameserver, as well as that of their parent nameserver. Why is
this?
- Why do you suppose the rules for nameservers in the Internet are so
stringent in the matter of off-site "replication" servers?
- What is a reverse lookup in the DNS, and why is it
regarded as a significantly harder problem than normal lookups?
- What is the significance of the fact that machine
luga.latrobe.edu.au
appears in an MX
RR (Resource Record) for machine
ironbark.bendigo.latrobe.edu.au
? What facility has to be
enabled on luga.latrobe.edu.au
for this to work?
- A nameserver query contains a parameter bit which is set to
1
if recursion is desired at the server and
0
otherwise. What would you expect to be the result of
queries in each of these situations?
- Research & discussion question: Most (all?) implementations of the
domain name system allow abbreviations of names so that, for
example, the name
ironbark
resolves to a correct address
for machines co-located at the Bendigo campus. How is this handled by the DNS,
and whereabouts is it implemented (ie, in the nameserver/s or in the
resolvers)? What about ironbark.bendigo
-- can this be
handled?
- Implementation question[2]:
The standard suggests that when a program needs to find the domain name
associated with an IP address, it should send an inverse query to the local
server first and domain
in-addr.arpa
only if that fails.
Why?
[1] Paraphrased from Comer,
Internetworking With TCP/IP, Vol 1, 3/e P404.
[2] ibid
See Prac #9 for the practical exercises accompanying this tutorial.
Copyright © 2003 by Philip
Scott, La Trobe University.