A1. What are the security implications
of these services?
In general terms your computer will be no more and no less secure than
it was before you started using the service. Unfortunately most personal
computers aren't very secure at all.
To access the service you usually run a client which is set up to connect
outwards. Unless the client is badly written, or contains a virus, there
is no reason why it should lower the security of your computer. The big
difference these services make is that your computer can now be found
(That's why you're using them remember), against that you can also be
found if you use IRC, ICQ, or connect to a web site, this just provides
robust way of finding you. If you're a home user, it's unlikely that you
will be targeted by the clever crackers who can get through almost any
security measure. Unless you have a computer savvy personal enemy, you
need to ask yourself why anyone would wish to target you. This faq is
about the services & is not a security primer, nor does it constitute
professional advice, however, before you connect to the internet you should
take reasonable steps to ensure that your PC is secure. This means you
- change all passwords from the default,
- install any security related updates posted by your software supplier,
- start taking regular back-ups (you should do this anyway), and
- only install those services you want to display for the outside world
A2. Why would I need one of these services?
You would use these services if you wanted to contact your computer over
the internet using a simple name which doesn't change, or if you wanted
to have a name you could give others this name.
A3. Why would I want to contact my computer?
If you run servers (e.g. ftp, www) on your computer you can retrieve files
from the computer when you aren't at home. Imagine you have written an
important report at home & when you get to work or school you find
that the disk you put it on is unreadable. By being able to find your
computer, you can retrieve files you have placed in the private part of
A4. Why would I want others to contact my computer?
You might want to make resources available to friends that you can't easily
place on a public web site. For example you might have an updateable database
which you allow them access to. These services are also useful if you
play multi player games on the internet. When you play against someone
else they need to be able to find you. Unless
they know your IP address they need help to find you. For some games you
connect to a server at a well known address, and for others you can directly
connect, the dynamic naming helps you make that connection.
A5. What are the different services?
These pages cover 3 different services: WWW redirection, dynamic subdomains,
and dynamic domain name hosting.
A6. WWW redirection
This is the simplest of the three services. It uses a property of the
WWW protocol (http) to forward page requests to your site. It only works
for web page lookup. Your computer may appear to the world to be a directory
on the services server (e.g. user xxx on service xyz.com might be www.xyz.com/dynamic/xxx)
or it might appear to be a separate computer in their network (e.g. user
xxx of service xyz.com, will appear to be at xxx.xyz.com). However it
appears, you have to remember that this service only works for
http://www.xyz.com/dynamic/xxx http://xxx.xyz.com type access. ftp, mail,
ping, games, etc usually won't work.
WWW based redirection comes in two forms: Frames Based and Browser Redirection. These are explained below.
There is no difference between the methods for your site (Although for
frames based services you might want to target the off page links to "_top").
Neither method supports bookmarking of internal pages, but the frames
based method does allow bookmarking of your front page. Frames Based Redirection
The service provider returns a <Frameset> page to the browser. The
main frame (often the only visible frame) in the returned page is on your
machine, and is but the surfer doesn't usually see the dotted quad address.
The service provider returns an instruction to the surfer's browser telling
it to change from the requested page on the provider's site to your dotted
A7. Dynamic subdomains
With a dynamic subdomain your computer's address will appear to the world
to be a part of the service's network. For example if you are user XXX
of service XYZ.com, your computer will appear to be at xxx.xyz.com. In
general terms any and all services you want to run on your computer are
fully compatible with this kind of service.
A8. Dynamic domain name hosting
Dynamic domain name hosting works with the same mechanism as Dynamic subdomains,
but instead of appearing to be part of the server's domain, your computer
seems to be it's own seperate entity. Everything you can run on a dynamic
subdomain will work on your dynamic domain name. With a dynamic domain
your computer will appear to the world as your registered domain. For
example I have registered the domain mydomain.com; when I stop writing
these pages & connect to a dynamic domain name host mydomain will
suddenly appear on the internet. There are only two issues with having
your own domain: You must register the name with the appropriate registry,
and you will probably need to make a provision for receiving email addressed
to the domain.
Registration is usually just a matter of sending dollars, pounds, guilders,
etc to someone, email is a little more tricky. To receive email you must
either run a smtp server, or arrange for a third party to handle mail
for you. Smtp servers are beyond the scope of these pages. If you are
running linux you probably have one already, if you are running Windows
or other operating systems check out an on-line library like Tucows or
A9. What do I need to do to setup a server on my computer?
That depends on the server. These days most come with reasonably straightforward
installation instructions. Check out library's like Tucows or Server Watch
to find what you need. If you are using a web server any of the dynamic
services will do. If you are using any other kind of service you probably
need either a dynamic subdomain, or dynamic domain name hosting.
A10. How can I start the service automatically when I connect to the Internet?
Some clients can be left running all the time, monitoring your Internet
connection. When they detect that you have connected, they automatically
advise the service provider. These can be set to start automatically when
you start, or log on to, your computer
If the client for your service doesn't do this, you may be able to use
another piece of software to automatically start the client. ICQ's netdetect
program can do this through it's launch list, or (Windows users only)
there is a product called Dunce available. There are almost certainly
similar products for other operating systems, consult your usual ownload
A11. What happens when I disconnect from the Internet?
All services will continue to hand out your last known address for a while.
Because of the way that DNS works, even if your service stops handing
out the address it may take a while for news of your disconnection to
propagate throughout the internet. People who attempt to access you during
this time will be directed to whoever has taken over your previous address.
This may, or may not, connect to a computer, and if it does that computer
may or may not have a compatible service.
A12. What is a domain name?
A Domain Name is a series of words which identify a computer, or series
of computers, on the internet. hkddns.com is a domain name, so is www.hkddns.com.
A13. What is dynamic IP?
Dynamic IP means that your numeric IP address is allocated for you by
an external provider, and it changes from time to time.
A14. How do domain names work?
The internet permits computers to communicate based on knowing a numeric
address for another computer. At its simplest, domain names are human
friendly aliases for these numbers. Software called a Domain Name Service
(DNS) translates the names into numbers. More information on the methods
used can be obtained here.
A15. What are these different record types in a DNS? What is an A Record?
An Address (A) record translates a human readable address like www.hkddns.com
into a numeric form like 220.127.116.11. Under the hood, these numbers are
what the internet really uses to find computers. Every computer which
can be located on the internet through a name is ultimately located by
using an A Record to translate its name into an address (Possibly after
first translating its name with a CNAME Record). What is a CNAME Record?
A CNAME (Cannonical name) allows one name to be an alias of another name.
For example, if I want my ftp and web sites to share a single computer,
and only want to maintain one A Record, then I can make one of these the
Cannonical Name for the other. What is an MX Record?
Put simply, an MX record tells a mail system which machine handles mail
for a given domain. Imagine you run BigCorp with several hundred machines
in the massivecorp.com domain. The chances are good that you will have
a single machine which handles all mail for your domain. In this case
you place an MX record in your DNS which says "Forward all mail for
bigcorp.com to the machine mail.bigcorp.com". Other computers which
wish to deliver mail to email@example.com retrieve this record from you
DNS & deliver the mail to mail.bigcorp.com.
A16. Will using these
services have any affect on my connection to the Internet?
Generally it won't, as the service providers are only supplying a name
which is used by the remote machine to find your PC. Some providers may
do something called ip tunneling which can slow down accesses through
their server. Obviously the remote machine which connects to you is going
to transfer some information (That's why you have this service, remember)
& this will take some of your available bandwidth while the transfer
A17. What happens
after that depends of the service you use.
Some services will continue to hand out your last known address until
time you connect. Some services require reasonably regular refreshing
of your address (That's part of what the client program is for), and after
a period the server will mark
you as not connected. Some services provide a mechanism to tell them that
you are leaving the internet. When you are shutting down your internet
connection this is well
worth using. If the service knows you are disconnected it may tell computers
connect to you that you don't currently have a valid address, or (usually
only useful for WWW) it may redirect them to another site you specify.
For example, my account redirects to one of my Hosting Company pages when
I am off-line.
A18. Will reverse IP lookups work?
It would take a lot of effort for the ISP to make reverse lookups work.
unlikely to do that work.