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Thread: How to configure for remote TCP/IP client conncections using MS Visual Basic OLE DB calls and PostgreSQL dll's?

How to configure for remote TCP/IP client conncections using MS Visual Basic OLE DB calls and PostgreSQL dll's?

From
John Edens
Date:

Hey guys, I'm trying to get a VB program to make a client connection to my PostgreSQL server running on an

Ubuntu 10.10 server.

 

Here's what I've done:

 

Client side - installed and registered the OLE DB .dll's from the PostgreSQL OLE DB Provider project.

 

server side -

 

the configuration described here: https://help.ubuntu.com/10.10/serverguide/C/postgresql.html

 

---------------

Have added this line to postgresql.conf:

 

 

listen_addresses = '*, 144.96.80.35, localhost'

 

I've also tried this as simply:

 

listen_addresses = '144.96.80.35, localhost'

 

also, port = 5432

 

--------------

 

I have added the following to pg_hba.conf:

 

 

# IPv4 local connections:

host    all         all         144.96.80.35  255.255.255.0         md5

local   all     postgres        md5

 

 

--------------

 

I've got the following code going in VB:

 

Public Class Form1

 

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        Const connString As String = "Provider=PostgreSQL; Server=144.96.80.35; User Id=postgres;Password=postgres;"

 

        Dim theOleDBconnection As New OleDb.OleDbConnection

 

        theOleDBconnection.ConnectionString = connString

 

 

        theOleDBconnection.Open()

    End Sub

End Class

 

So when the project opens up, it should make the connection and display the form.

 

What happens is that I get an error...

 

OleDbException was unhandled

 

could not connect to server: Connection refused (0x0000274D/10061)

               Is the server running on host "" and accepting

               TCP/IP connections on port 5432?

 

---------------------------

 

So, obviously I've got something configured incorrectly.

 

I'm troubled that the VB error seems to show a null value for the host. Shouldn't that be the Server value in

the connection string?

 

Thanks to all for any help…

Re: How to configure for remote TCP/IP client conncections using MS Visual Basic OLE DB calls and PostgreSQL dll's?

From
Steve Crawford
Date:
On 03/09/2011 07:31 AM, John Edens wrote:

Hey guys, I'm trying to get a VB program to make a client connection to my PostgreSQL server running on an

Ubuntu 10.10 server....

 

listen_addresses = '*, 144.96.80.35, localhost'


Using * should be fine unless you have multiple IP addresses and want the *server* to *listen* on only some of those addresses - say localhost if you were running web and db on the same machine and didn't want to listen to connections from the outside. This setting only determines where the server listens.

 

I have added the following to pg_hba.conf:

 

 

# IPv4 local connections:

host    all         all         144.96.80.35  255.255.255.0         md5

local   all     postgres        md5

 

This setting determines what *clients* are allowed to connect to the server. Your setting here is strange. It should be a proper network range. You have an IP address with a class-C netmask.

If you want to only accept connections from a specific single IP address, use 144.96.80.35/32 or 144.96.80.35 255.255.255.255. But if you want to listen to the class-C then 144.96.80.0/24 or 144.96.80.0 255.255.255.0.

And since the IP address you gave appears real since it is in the assigned public space for Stephen F. Austin State University, I hope this machine is hiding behind a firewall.

Cheers,
Steve


Re: How to configure for remote TCP/IP client conncections using MS Visual Basic OLE DB calls and PostgreSQL dll's?

From
John Edens
Date:

------------

Using * should be fine unless you have multiple IP addresses and want the *server* to *listen* on only some of those addresses - say localhost if you were running web and db on the same machine and didn't want to listen to connections from the outside. This setting only determines where the server listens.

-------------

 

Okay, done that - what is the difference between  listening on only some of those addresses and allowing only clients in a certain range to connect?

 

 

------------

And since the IP address you gave appears real since it is in the assigned public space for Stephen F. Austin State University, I hope this machine is hiding behind a firewall.

------------

 

Yes, behind a firewall and also that machine is a brand new linux box that literally has nothing else on it besides a new install of PostgreSQL

 

But, yeah, should have anoned up the address...

 

Re: How to configure for remote TCP/IP client conncections using MS Visual Basic OLE DB calls and PostgreSQL dll's?

From
Steve Crawford
Date:
On 03/09/2011 09:54 AM, John Edens wrote:

------------

Using * should be fine unless you have multiple IP addresses and want the *server* to *listen* on only some of those addresses - say localhost if you were running web and db on the same machine and didn't want to listen to connections from the outside. This setting only determines where the server listens.

-------------

 

Okay, done that - what is the difference between  listening on only some of those addresses and allowing only clients in a certain range to connect?

 

They are completely different.

Your server can have multiple IP addresses. In fact, it almost certainly has an IP assigned to your NIC and a localhost address. But you could have multiple NICs in the machine and/or multiple IP addresses assigned to each NIC. This is very common - especially for web servers hosting several sites on different addresses. The addresses can be on different networks, as well.

Suppose your server has addresses 10.1.1.2, 10.1.1.3 and 192.168.1.4. If listen_addresses is set to *, a client could connect to PostgreSQL by connecting to any of those addresses - i.e. the host in their connection string could be any of the addresses you listen on. If that is not what you want, you need to explicitly list the addresses you want PostgreSQL to use.

Now that you are listening on one or more addresses, the pg_hba.conf determines who is allowed to connect. It is completely independent of where you listen. It could include all IP addresses, or one or more individual IPs or IP ranges. And the IP addresses allowed for clients do not need to overlap your listen_address or be on the same IP network.

By way of example, you could have three independent instances of PostgreSQL running on your machine - perhaps one for dev, one for QA and one for deployment-staging. You could have dev listen only on .2, QA on .3 and deploy on .4. You could even have a 4th, say "sandbox", listening on all (though it would have to have a different port). And each one of those instances could have different pg_hba.conf settings to restrict client access as appropriate.

Cheers,
Steve

Re: How to configure for remote TCP/IP client conncections using MS Visual Basic OLE DB calls and PostgreSQL dll's?

From
John Edens
Date:

Thanks for that explanation, Steve. This is my first time doing much of anything with a server, so that’s all good to know!

John

 

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Your server can have multiple IP addresses. In fact, it almost certainly has an IP assigned to your NIC and a localhost address. But you could have multiple NICs in the machine and/or multiple IP addresses assigned to each NIC. This is very common - especially for web servers hosting several sites on different addresses. The addresses can be on different networks, as well.
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