Many (most ?) people these days have a router/switch/wireless box on their
end of a broadband internet connection which they use to allow multiple
computers to access the Internet. Almost all of these devices offer some
form of NAT
>From CISCO ...
Static NAT - Mapping an unregistered IP address to a registered IP address
on a one-to-one basis.
Dynamic NAT - Maps an unregistered IP address to a registered IP address
from a group of registered IP addresses. Dynamic NAT also establishes a
one-to-one mapping between unregistered and registered IP address, but the
mapping could vary depending on the registered address available in the
pool, at the time of communication.
Overloading - A form of dynamic NAT that maps multiple unregistered IP
addresses to a single registered IP address by using different ports.
Known also as PAT (Port Address Translation), single address NAT or
port-level multiplexed NAT.
ie you might have
Externally Internally
213.12.15.16:21 192.168.32.10:21 ie FTP
213.12.15.16:80 192.168.32.11:80 ie HTTP
213.12.15.16:1234 192.168.32.12:2345 ie your "server"
NB Most of the smaller/cheaper broadband routers utilise "overloading".
As a result of all of this, you "cannot" assume that a client can
communicate with your server based on the parameters detectable at the
server. It cannot know that its address (and possibly port) is being
translated.
Therefore, you need to incorporate a configuration form into which a user
can enter the necessary IP-address and port details.
(info available via your "web server"/"support section" ...., etc)
An added complication is the assignment of the external address(es) by the
ISP - if dynamic, then these addresses can (and usually do) change. One
possible way around this is to utilise a service like DYNDNS.ORG and always
refer to your server IP-address by that name (rather than using the actual
IP address).
Again, as someone has already mentioned - check your ISP broadband contract
to what "server" functionality you are allowed to implement .......
Regards,
Brian
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
On Behalf Of Francois Piette
Sent: Monday, 15 May 2006 9:55 PM
To: Delphi-Talk Discussion List
Subject: Re: designing a simple P2P application - server side
> For the moment I will ignore them because I want
> to see my application working at least for
> peoples who have a 'normal' internet connection.
NAT routers are becoming - if not already - the "normal" connection type !
> Later I will see how can this NAT problem can be solved.
> I know something about a NAT translate
> the IP but I have no idea how this can be overcome but
> I will start looking in to it.
Most NAT routers have "port forwarding" which is the solution to your
problem. But the "normal" user has no idea about how to configure their
router ! And since there is no standard, you'll be exposed to big
difficulties.
> Also you are right about accessing the list from the server. Obvious I
need some kind of script to
> handle the requests form the clients. I don't know too much PHP but I
think I will find a friend
> to write it for me.
You can write the scripts using Delphi or other languages. BUT first ask
your provider what you are allowed to use for the price you pay.
Contribute to the SSL Effort. Visit http://www.overbyte.be/eng/ssl.html
--
[EMAIL PROTECTED]
Author of ICS (Internet Component Suite, freeware)
Author of MidWare (Multi-tier framework, freeware)
http://www.overbyte.be
----- Original Message -----
From: "Human" <[EMAIL PROTECTED]>
To: "Delphi-Talk Discussion List" <[email protected]>
Sent: Monday, May 15, 2006 11:54 AM
Subject: Re: designing a simple P2P application - server side
> Dear Francois,
> thank you very much for your ideas. I totally forgot about the NAT
routers. I never worked with a
> NAT router but I know they are dificult devices and lots of programs have
problems to pass through
> them.
> For the moment I will ignore them because I want to see my application
working at least for
> peoples who have a 'normal' internet connection.
> Later I will see how can this NAT problem can be solved. I know something
about a NAT translate
> the IP but I have no idea how this can be overcome but I will start
looking in to it.
>
> Also you are right about accessing the list from the server. Obvious I
need some kind of script to
> handle the requests form the clients. I don't know too much PHP but I
think I will find a friend
> to write it for me.
>
> I intended to use your ICS. That package is plain great. I didn't put to
much internet oriented
> code in my programs until now but I made few experiments with ICS and I
really like it.
> And what the heck, if I can make this work, I will donate the code to ICS.
>
>
>
> =============================================
>
>
>
> Cosmin Prund informed me that using the reply button doesn't work to creat
a new thread.
> I want to appologise to every one who use an email client for inconvenince
for messing up the
> order of the threads.
> I didn't know about this issue, since I am subscribed to this list using
my Yahoo account which
> can't be read by my email client (Thunderbird).
> I never use my real email address for places where it might be made
public. I already receive
> 100-150 spam emails every day on this 'public' email address.
>
> ( http://en.wikipedia.org/wiki/Thread_hijacking )
>
>
>
> =============================================
>
>
>
>
>
>
> --- Francois PIETTE <[EMAIL PROTECTED]> wrote:
>
> > > The difficulty is to make the clients aware of each other.
> >
> > IMO the most difficult thing is to have a client connect to another one
> > which is behind a NAT router or a firewall.
> > NAT routers are very very common these days.
> >
> > > Until now my idea is keep a txt file on the server with RW rights
where a
> > > client will write its
> > > own IP when it enters the network and delete its own address when it
> > > leaves the network.
> >
> > Better to use a standard web server with a few scripts (PHP, ASP or even
> > Delphi depending on the hosting possibilities).
> > One script will update the IP list, the other will download it. Use a
> > timestamp in the list to clean it if a client doesn't do anything for
some
> > time.
> > Your client could use ICS HTTP client (http://www.overbyte.be) to
> > query/update the webserver, using the script you'll design. Quite easy.
> >
> > > 7. I estimate that the maximum number of users in this moment is 50000
and
> > > rising (considering the
> > > number of downloads per day) so I think there won't be more than 20000
> > > simultaneous connected
> > > users at a moment of the day.
> >
> > With a webserver, you don't have persistant connections. So what really
> > count is how many will query the server at the same time given the fact
that
> > the script accessing the file will execute during - for example - half a
> > second. I guess you'll only have a handful of simultaneous connections
to
> > the server.
> >
> > > This will generate a list of aprox 0.5MB which is too big.
> >
> > You need 4 bytes per IP and probably 4 bytes for time stamp. This gives
a
> > list of 160 KB.
> > You can keep the time stamp in another file. So the size will be 80 KB
for
> > IP only.
> >
> > > So if you have any better idea please let me know.
> >
> > You can send only updates to the connecting client. The clients could
say:
> > "Hey server give me all changes since this time". This would
dramatically
> > reduce the size.
> >
> > Contribute to the SSL Effort. Visit http://www.overbyte.be/eng/ssl.html
> > --
> > [EMAIL PROTECTED]
> > The author for the freeware multi-tier middleware MidWare
> > The author of the freeware Internet Component Suite (ICS)
> > http://www.overbyte.be
> >
> >
> >
> > ----- Original Message -----
> > From: "Human" <[EMAIL PROTECTED]>
> > To: "Delphi-Talk Discussion List" <[email protected]>
> > Sent: Sunday, May 14, 2006 1:32 PM
> > Subject: designing a simple P2P application - server side
> >
> >
> > > Hello.
> > > I want to write a simple P2P module (for one of my existing
applications
> > > application) specialized
> > > in transferring small files (max 0.5 or 1 MB) but I would like not to
keep
> > > a central server.
> > > A P2P network without server is difficult to realize so I think I
really
> > > need a minimum central
> > > server.
> > > The difficulty is to make the clients aware of each other.
> > > Until now my idea is keep a txt file on the server with RW rights
where a
> > > client will write its
> > > own IP when it enters the network and delete its own address when it
> > > leaves the network.
> > > Any client connected to the network will read that file to know who
else
> > > it present in the
> > > network.
> > > In this moment the clients won't need the server anymore. They connect
to
> > > each other directly and
> > > start the download.
> > >
> > > Items and issues:
> > > 0. The server is running Windows but it is not mine so I can't write
my
> > > own custom software
> > > (although I think they allow my to write and install small .Net
> > > application on their server)
> > > 1. Every client must renew its IP (and timestamp) in the server's list
> > > every at 3 hours
> > > 2. It must download a new IP list at every 20 minutes
> > > 3. The list must be small
> > > 4. What will happen if 2 clients will simultaneously try to write to
the
> > > list?
> > > 5. What happens when a client suddenly leave the network without
deleting
> > > its IP from the list
> > > (probably the list must be cleaned by a special utility)
> > > 6. Idea: when a client enters the network it can send a message to
every
> > > already connected client
> > > to inform them about its presence so they don't need to re-download
the
> > > list too often from the
> > > server.
> > > 7. I estimate that the maximum number of users in this moment is 50000
and
> > > rising (considering the
> > > number of downloads per day) so I think there won't be more than 20000
> > > simultaneous connected
> > > users at a moment of the day. This will generate a list of aprox 0.5MB
> > > which is too big. So in
> > > order to decrease the download:
> > > -compression needed
> > > -more than a list is required
> > >
> > > So if you have any better idea please let me know.
> > >
> > >
> > > If I choose Christianity then the Islamic will say I'm a pagan.
> > > If I choose Islamic then the Buddhism will say I'm a pagan.
> > > If I chose Buddhism then the Jewish will say I'm pagan.
> > > If I choose no God then everybody will say I'm pagan.
> > > Please, can I be free? Can you NOT tell me how I should live MY life?
> > >
> > > __________________________________________________
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> > > Tired of spam? Yahoo! Mail has the best spam protection around
> > > http://mail.yahoo.com
> > > __________________________________________________
> > > Delphi-Talk mailing list -> [email protected]
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> >
> > __________________________________________________
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> >
>
>
> If I choose Christianity then the Islamic will say I'm a pagan.
> If I choose Islamic then the Buddhism will say I'm a pagan.
> If I chose Buddhism then the Jewish will say I'm pagan.
> If I choose no God then everybody will say I'm pagan.
> Please, can I be free? Can you NOT tell me how I should live MY life?
>
> __________________________________________________
> Do You Yahoo!?
> Tired of spam? Yahoo! Mail has the best spam protection around
> http://mail.yahoo.com
> __________________________________________________
> Delphi-Talk mailing list -> [email protected]
> http://www.elists.org/mailman/listinfo/delphi-talk
__________________________________________________
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