Networking works from computer A to computer B, but not vice versa ?!?

[larkmore]

Just starting to learn networking, and this may not be a Java question
so much as a Windows environment question. I've written a little
server program that waits for a client to connect and then spits some
data to the client. Both the client and the server work fine running
on the same computer. If I run the client on computer A and the
server on computer B, they behave properly. However, if I run the
client on computer B and the server on computer A I cannot establish a
connection between the two. Is there some easy way to figure out what
is going on? I tried using different port numbers for the server to
no avail. As far as I know there are no firewall programs installed
on either machine. Both are running WinXP Pro. and using v1.4.2_08
for the JRE/SDK. Any ideas?

 

[Knute Johnson]

Just starting to learn networking, and this may not be a Java question
so much as a Windows environment question. I've written a little
server program that waits for a client to connect and then spits some
data to the client. Both the client and the server work fine running
on the same computer. If I run the client on computer A and the
server on computer B, they behave properly. However, if I run the
client on computer B and the server on computer A I cannot establish a
connection between the two. Is there some easy way to figure out what
is going on? I tried using different port numbers for the server to
no avail. As far as I know there are no firewall programs installed
on either machine. Both are running WinXP Pro. and using v1.4.2_08
for the JRE/SDK. Any ideas?

I would still suspect a firewall somewhere. Are you really running
Windows without a firewall?

 

[CodeForTea]

I would still suspect a firewall somewhere. Are you really running
Windows without a firewall?

Try telnet to connect.

Dinesh

 

[Brandon McCombs]

Just starting to learn networking, and this may not be a Java question
so much as a Windows environment question. I've written a little
server program that waits for a client to connect and then spits some
data to the client. Both the client and the server work fine running
on the same computer. If I run the client on computer A and the
server on computer B, they behave properly. However, if I run the
client on computer B and the server on computer A I cannot establish a
connection between the two. Is there some easy way to figure out what
is going on? I tried using different port numbers for the server to
no avail. As far as I know there are no firewall programs installed
on either machine.

That doesn't mean there still isn't a firewall that is preventing the
connection from being established. XP has a builtin firewall that has to
be turned off within the properties of the LAN connection and I believe
it is on by default. Make sure that is off and then try your connection
(note the firewall will allow outbound but not inbound so that's why it
would work for you going out of computer A as a client but not coming
into it as a server).

 

[larkmore]

Bingo. I guess I either forgot or never knew that XP had a firewall
by default. Strange that only one of the machines had it turned on.
But it works now. Thanks!
-Will