October Newsletter
Virus of the month
The Fanbot worm emerged on 17th
October and is currently assessed as a
medium threat, although it carries
the hallmarks of a virus that could
become widespread. It lowers the
security settings of infected computers
and generates fake error messages. It's
known to spread via its own email engine
and via many popular peer to peer
programs. Take the usual precautions
with downloading files and opening email
attachments.
The Domain Name
System
If you’ve networked any computers
together or spent much time on the
internet, you will probably have come
across an IP address. This is the series
of four numbers, each consisting of up
to three digits separated by dots, which
identifies any computer on the network.
Only networks using the TCP/IP protocol
use IP addresses, but as this includes
the internet, you are more than likely
to have used a PC with an IP address,
even if you weren’t aware of it at the
time.
Current IP addresses are of the form
168.192.0.1, where each number can be
anything between 0 and 255. The system
works well, because it is independent of
platform, so PCs using Windows can
network happily with those running
Linux. They are equally happy talking to
Macs and any other operating system that
supports TCP/IP. This is important
because the fundamental strength of the
internet is that pretty much any
computer can join it.
However, there is a downside. People
find strings of numbers difficult to
remember and hard to type flawlessly.
This is why the domain name system was
created. Domain name servers translate
IP addresses into domain names and vice
versa. This means you can access
information from a computer on the net
without knowing its IP address. The web
or email address you use contains enough
information for a domain name server to
route it correctly.
The domain name system works as a
hierarchy. The world root is the dot,
from which all domains are derived. The
letters immediately after the last dot
donate the Top Level Domain or TLD. This
may be generic, such as .com or .org, or
country specific, such as .uk. Country
specific top level domains consist of
two letters that generally relate to the
internationally agreed list of country
codes. This would dictate that the UK
should be denoted as .gb, but the .uk
domain had been in use for a number of
years and changing all present domain
names seemed a needlessly disruptive
task, so .uk remains the country code
top level domain for Great Britain and
Northern Ireland.
There are hundreds of country code top
level domains, but less than fifteen
generic top level domains. There is
constant debate about increasing the
number of these, but there is a need to
keep the number of generic TLDs to a
manageable number. This is so that most
people have some idea of what the top
level domain means. If the codes spiral
upwards, it becomes much harder for
people to remember what they are.
It would be quite a feat of memory to
remember all the country code TLDs, but
you can get some clue from the number of
letters after the last dot. All country
codes consist of two letters, whereas
generic top level domains are three or
more letters. Once you know you are
dealing with a country code, you can
look it up via any online database, such
as the one available at
www.norid.no/domenenavnbaser/domreg.html.
One cautionary word though. Just because
a website is reached via a country code
domain name, there is no guarantee that
the site is hosted in that country or
that the organisation or individual has
much of a presence there. Each country
code TLD is managed by its own registry,
each of which has its own rules and
regulations. While providing a contact
address in the country involved is a
normal requirement for registering a
domain name, be aware that this could be
a forwarding address. The global nature
of the internet can be used to muddy the
waters somewhat.
Most top level domains contain second
level domains. A domain name like
supportpcs.co.uk belongs to the second level
domain .co.uk and is managed here by
Nominet UK. However, you may have come
across web addresses ending in .uk.com.
or .uk.net. These aren’t administered by
Nominet UK but by CentralNic, who offer
a range of “alternative” domain names
that aren’t subject to local rules and
regulation.
Once you’ve entered a web address into
your browser, this address needs to be
converted into the IP address of the
computer that is hosting that site. The
web browser sends a request to the
nearest domain name server. If the
server has handled the request before,
it finds the relevant address in its
cache and passes it on. If the domain
name is new or the server hasn’t handled
it for some time, the request gets
passed on to a different domain name
server further up in the hierarchy than
itself. If necessary, the request keeps
being passed on until the information is
found. If this continues for too long,
your browser drops the connection and
responds with a file not found message.
If the domain name is resolved, the IP
information is returned to your browser
and you connect to the computer hosting
the website. On occasions you may
receive the file not found message when
in fact it has simply taken too long for
the various domain name servers to
locate the information. It is worth
trying again as one of the domain name
servers may well have received the
address information since your earlier
attempt and hold the information in its
cache. However, it is also worth noting
that the most common cause for browsers
to return a file not found message is
mistyping the web address.
So, domain names are handled by a number
of servers, each of which is connected
to the others so that information can be
shared and replicated, ensuring that the
system stays up and running even if one
or more of these computers goes down.
Top level domains are each managed by a
registry. These may handle generic top
level domains or country code TLDs. Most
of these are sub divided into second
level domains. You browser asks nearby
domain name servers to resolve each
domain name request into an IP address
to allow your PC to connect to the
hosting site. |
