Creating a TCP/IP connection on already-networked computers

[John Salerno]

Let me see if this question even makes sense...I'm reading Core Python
Programming and I jumped ahead to the more specific topics like network
programming. I plan to follow along with the example in that chapter and
create a socket connection between my desktop and laptop.

However, these two computers are already connected on my home network
(using the Windows Network Setup Wizard), so I was wondering if this
will have any effect on what I might try to do with Python. In other
words, if the program I write actually works and allows the two
computers to speak to each other, will that be a result purely of the
program, or will it have anything to do with the fact that they are
already on a home network together? (i.e. there's another variable in play?)

Thanks.

[Grant Edwards]

On 2008-06-14, John Salerno <jo******@gmail NOSPAM.comwrote :

Let me see if this question even makes sense...I'm reading
Core Python Programming and I jumped ahead to the more
specific topics like network programming. I plan to follow
along with the example in that chapter and create a socket
connection between my desktop and laptop.

However, these two computers are already connected on my home
network (using the Windows Network Setup Wizard), so I was
wondering if this will have any effect on what I might try to
do with Python.

I don't know the example programs you're talking about, but
it's a pretty good bet that the example programs won't work if
the two computers can't reach each other using IP networking.

In other words, if the program I write actually works and
allows the two computers to speak to each other, will that be
a result purely of the program, or will it have anything to do
with the fact that they are already on a home network
together? (i.e. there's another variable in play?)

The two Python programs won't be able to communicate with each
other unless the two computers are already set up on network(s)
that allow the routing of IP packets between the two computers.
I presume that's what the "Network Setup Wizard" did (set up IP
networking), but I don't really do windows (I especially don't
do "Wizards" if I can avoid it).

--
Grant Edwards grante Yow! Alright, you!!
at Imitate a WOUNDED SEAL
visi.com pleading for a PARKING
SPACE!!

[John Salerno]

John Salerno wrote:

if the program I write actually works and allows the two
computers to speak to each other, will that be a result purely of the
program, or will it have anything to do with the fact that they are
already on a home network together?

Here are the two programs. Server first, then client. They work, which
in itself amazes me that it's so simple to create a network connection
like this! But my basic question is this: would this connection work if
the two computers (each running one of these scripts) were completely
unrelated to one another? My two are on a home network, but if I were to
run the server program and have a friend of mine (who lives somewhere
else) run the client program, would it still work?

-----
#!/usr/bin/env python

from socket import *
from time import ctime

HOST = '192.168.1.100'
PORT = 21567
BUFSIZ = 1024
ADDR = (HOST, PORT)

tcpSerSock = socket(AF_INET, SOCK_STREAM)
tcpSerSock.bind (ADDR)
tcpSerSock.list en(5)

while True:
print 'waiting for connection...'
tcpCliSock, addr = tcpSerSock.acce pt()
print '...connected from:', addr

while True:
data = tcpCliSock.recv (BUFSIZ)
if not data:
break
tcpCliSock.send ('[%s] %s' % (ctime(), data))

tcpCliSock.clos e()

tcpSerSock.clos e()
-----

-----
#!/usr/bin/env python

from socket import *

HOST = '192.168.1.100'
PORT = 21567
BUFSIZ = 1024
ADDR = (HOST, PORT)

tcpCliSock = socket(AF_INET, SOCK_STREAM)
tcpCliSock.conn ect(ADDR)

while True:
data = raw_input('')
if not data:
break
tcpCliSock.send (data)
data = tcpCliSock.recv (BUFSIZ)
if not data:
break
print data

tcpCliSock.clos e()
-----

[John Salerno]

John Salerno wrote:

-----
#!/usr/bin/env python

from socket import *
from time import ctime

HOST = '192.168.1.100'

-----
#!/usr/bin/env python

from socket import *

HOST = '192.168.1.100'

A question about this. Is the "HOST" referring to the IP address of the
server computer in both of these cases? Because when I ran the program
and got to the part where it says "connected from:" on the server side,
it shows this same IP address. Shouldn't it be something different,
since the requests are coming from a different computer than the server
computer?

[Grant Edwards]

On 2008-06-14, John Salerno <jo******@gmail NOSPAM.comwrote :

John Salerno wrote:

>if the program I write actually works and allows the two
computers to speak to each other, will that be a result purely of the
program, or will it have anything to do with the fact that they are
already on a home network together?

Here are the two programs. Server first, then client. They work, which
in itself amazes me that it's so simple to create a network connection
like this! But my basic question is this: would this connection work if
the two computers (each running one of these scripts) were completely
unrelated to one another?

That depends on your definition of "unrelated. "

My two are on a home network, but if I were to run the server
program and have a friend of mine (who lives somewhere else)
run the client program, would it still work?

Yes, if the routers/firewalls/PCs were set up properly and if
you changed the IP addresses in the programs appropriately.

--
Grant Edwards grante Yow! I want the presidency
at so bad I can already taste
visi.com the hors d'oeuvres.

[Grant Edwards]

On 2008-06-14, John Salerno <jo******@gmail NOSPAM.comwrote :

John Salerno wrote:

>-----
#!/usr/bin/env python

from socket import *
from time import ctime

HOST = '192.168.1.100'

>-----
#!/usr/bin/env python

from socket import *

HOST = '192.168.1.100'

A question about this. Is the "HOST" referring to the IP
address of the server computer in both of these cases?

Yes.

Because when I ran the program and got to the part where it
says "connected from:" on the server side, it shows this same
IP address.

Then you must have been either running the client program on
the same machine as the server program or you've got some sort
of NAT/port-forwarding going on.

Shouldn't it be something different, since the requests are
coming from a different computer than the server computer?

Works fine for me. When I run the client program on a machine
different than the server program, the server program prints
out "connected from:" and then the client machine's IP address.

--
Grant Edwards grante Yow! Maybe I should have
at asked for my Neutron Bomb
visi.com in PAISLEY --

[John Salerno]

Grant Edwards wrote:

>Shouldn't it be something different, since the requests are
coming from a different computer than the server computer?

Works fine for me. When I run the client program on a machine
different than the server program, the server program prints
out "connected from:" and then the client machine's IP address.

Hmm, so could the reason that the client request is shown to be coming
from the same IP address as the server machine be that they are on the
same home network?

I guess to truly test my question, I need to have two computers that are
completely "unrelated" to one another -- meaning they are in no way
connected via any type of network prior to running these scripts.

[John Salerno]

Grant Edwards wrote:

That depends on your definition of "unrelated. "

Heh heh, you mean that wasn't specific enough!? :)

I just mean completely unconnected in any possible way, network or
otherwise.

>My two are on a home network, but if I were to run the server
program and have a friend of mine (who lives somewhere else)
run the client program, would it still work?

Yes, if the routers/firewalls/PCs were set up properly and if
you changed the IP addresses in the programs appropriately.

Ok, that's basically what I was curious about. Since my two computers
are already on a network, I couldn't be positive that this wasn't
allowing them to connect, rather than the two client/server scripts.

[Grant Edwards]

On 2008-06-14, John Salerno <jo******@gmail NOSPAM.comwrote :

Grant Edwards wrote:

>>Shouldn't it be something different, since the requests are
coming from a different computer than the server computer?

Works fine for me. When I run the client program on a machine
different than the server program, the server program prints
out "connected from:" and then the client machine's IP address.

Hmm, so could the reason that the client request is shown to be coming
from the same IP address as the server machine be that they are on the
same home network?

No, not for the usual value of "on the same home network".
I've no idea how your home network is set up, so that's about
all I can say.

I guess to truly test my question, I need to have two
computers that are completely "unrelated" to one another --
meaning they are in no way connected via any type of network
prior to running these scripts.

If the two computers are in no way connected via any type of
network, then the two programs won't be able to talk to each
other.

The programs can't create a network, they can only use one that
already exists.

--
Grant Edwards grante Yow! I've got an IDEA!!
at Why don't I STARE at you
visi.com so HARD, you forget your
SOCIAL SECURITY NUMBER!!

[Grant Edwards]

On 2008-06-14, John Salerno <jo******@gmail NOSPAM.comwrote :

Grant Edwards wrote:

>That depends on your definition of "unrelated. "

Heh heh, you mean that wasn't specific enough!? :)

I just mean completely unconnected in any possible way, network or
otherwise.

If they're completely unconnected in any possible way, then I
take that to mean that any communication between the two
computers is impossible.

--
Grant Edwards grante Yow! I demand IMPUNITY!
at
visi.com