Networks·41,424 discussions

Why i can’t telnet a particular port even if the port(tcp) is open

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I’m having a problem connecting to some clients running WinXP via a particular port(tcp). The port has been opened at the windows firewall. Everything seems ok. I could PING-no problem. But when i try to telnet that particular port, it failed. Can someone please tell me what could be the possible reasons.

Topic

Clarifications

In reply to Why i can’t telnet a particular port even if the port(tcp) is open

Clarifications

Host Configuration

In reply to Why i can’t telnet a particular port even if the port(tcp) is open

Is the host computer your trying to telnet into configured to use the port for telnet. Allowing a different telnet port through the windows firewall doesn’t configure the service to use the different port.

Actual Scenario

In reply to Host Configuration

My scenario:-I’m at the server.I’m supposed to connect with a client from the server using a particular port. The server was initially configured to accept the communication via this particular port. But then when i try to communicate, it fails saying that the port was not configured at the client. Upon remotely logging into the client’s pc, i checked the windows f’wall and found that it was already open.Any suggestion pal?

client

In reply to Actual Scenario

On the client side, the service needs to be set up to use the specified port. The fact that the client has it open in the firewall doesn’t mean that it is configured in the service. Also, it doesn’t matter how the server you’re connecting from is configured; in general you specify a port when connecting to a host. Chances are that if the client hasn’t been configured to use a different port, you could open port 23 in the firewall and connect to it.

I’m going to guess that the client is running XP Pro, but correct me if I’m wrong. Make sure the client has the telnet server service running and not just the client.

The fact of the matter is that the client needs to be configured to accept communication on the particular port. The servers configuration is irrelevant, just make sure it’s set to connect to the host on the host’s configured port.

Client using XP Pro

In reply to client

XP Pro is right.

Referring to your quote, “Make sure the client has the telnet server service running and not just the client”, how and where do i configure the service.

I tried run->services.msc->and then started the telnet service. Were you reffering to this step? I tried this step but it still doesn’t communicate. Is there another step?

Thats right.

In reply to Client using XP Pro

Thats the right step. Now, temporarily open up port 23 on the firewall and try to telnet in, just don’t leave it open. Do this to test and see if everything is functioning correctly.

To change the port on the telnet server service, which you already have enabled, you must open the registry, so regedt32 or regedit.

Navigate to:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\TelnetServer\1.0.\

When you click on the 1.0 look in the main window and you’ll find the entry TelnetPort, double click on it. Now remember, change the radio button to decimal, otherwise it says 17.

So go ahead and do either of the steps first, I didn’t have a computer to test the registry settings before so I couldn’t post it earlier, sorry bout that. Anyway you can go ahead and change the port without doing the first step I mentioned, if you want. Let me know how things go.

Will try the regedit step

In reply to Thats right.

PoBody, i really appreciate your assistance.
I am still trying out the registry edit step that you’ve suggested to me yesterday. I will let you know if it works.

Thanks Pal.

Anytime

In reply to Will try the regedit step

Hey, anytime, I’m here to help. So, let me know how things work out. Hopefully the registry step solves the problem.

On another note, what are you trying to accomplish on the client with the use of telnet? I understand that its more a of a quick and easy solution, but what are you trying to accomplish on the client? The reason I ask is that telnet is very insecure compared to some of the other options that are comparably easy to set up; for instance, ssh. If your interested in a more secure option, perhaps I can help; you can contact me on this topic if you wish.

Hope things are working, just glad I could help. Let me know if theres anything else I can help you with.

unsuccessful

In reply to Why i can’t telnet a particular port even if the port(tcp) is open

My company is a antivirus solution provider. We actually need to support(push updates & renew license) to our clients’ pc from our dedicated antivirus server. In order for the server to communicate with the client’s pc, both sides need to open a couple of pre-determined ports. Supposedly, all of the clients’ pc is manegable from our server.

Just a remaining few clients’ pc is NOT manegable.The connectivity is there as the PING result was successfull. But when i “telnet ” from the cmd prompt, it fails.

When i remotely logged into the client’s pc, i notice that the required ports has already been open.

PoBody,your suggestion was to start the Telnet service and to edit the registry at client’s pc. I’m slightly confused pal.

1)In the regedit do i need to change the
hexadecimal-17 to decimal-23(or they are
both the same)?
2)Must i edit the registry for both client
and server?
3)Must i start the telnet service for both
client and server?
4)In certain cases, the access to the registry is denied even when using an administrator account

Almost there

In reply to unsuccessful

You’ve got the right steps down.

1. When you open the key it shows up as 17
with the hexidecimal button selected. You
don’t want to change this number. If your
going off a general port number it will be
in decimal not hexidecimal. So click the
circle next to the decimal setting and the
number changes to 23. This is the number
you want to change to whatever port number
you use for telnet sessions.

2. You should only need to edit the client
machine. On the server you will specify the
port to use in the command to connect, just
as you have it specified above.

3. You only need to start the clients
telnet service. Also, you might want to
make sure the service is automatic, unless
you want to start the service every time
the computer restarts. when you type telnet
in the command prompt on the service you’re
invoking the telnet client, which doesn’t
require the telnet service.

4. Hmm, I guess it’s possible theres an
anti-spyware or similar program
thats “protecting” the registry, but
offhand I’m not too sure. Try
both ‘regedit’ and ‘regedt32’ when this
happens.

On another note, using the telnet service
is openeing up computers to many
vulnerabilities. I usually wouldn’t
recommend it. It doesn’t take much to
determine which ports are open, and for
which services they are open for. Telent
has some vulnerabilities, not to mention it
is unecrypted, all data passed through is
clear text. If your company is using this
service, I’d imagine this would have come
up already, and I don’t mean to judge. One
of my main interests is security, so,
naturally, I’d have some conern.

Hope this clears it up. Let me know how it
goes.

I’m clear

In reply to Almost there

Thanks pal for your detail explanation. I’m very clear now. Just waiting to test it on the client. Will let you know on the progress.

Thnks once again for all your time and effort.

[Author]

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