ISP blocking ports

Unless you are a customer of the Norwegian ISPs Get or Telenor, this post will only be a general guide to what your ISP might or might not do to your connection. It should be a part of your consideration when troubleshooting an internet link that does not seem to do what you think it should.

After transferring from Telenor to Get as my internet service provider, I noticed that some of my mail accounts would not let any mail through anymore. As I discovered, there were no response from any SMTP mailserver but one, namely Gets own SMTP server. Telenor also blocks communication to other servers than their own over TCP port 25 (SMTP), but at least there is a choice to switch this extra filtering off via your user webpages. When contacting Get about the same feature, after a loong wait, they responded that they are blocking all of the following ports to their customers:

21          TCP         FTP         In
25 *        TCP         SMTP        In and out (except Get)
69          UDP         TFTP        In and out
80          TCP         WEB/http    In
137-139     TCP/UDP     NetBios     In and out
161         UDP         SNMP        Out
548         TCP         AFPoverTCP  In
12345       ICMP/TCP    Netbus      In and out
27374 *     TCP         ASP         In and out

ASP above means Address Search Protocol, not Active Server Pages, in this list.

It is an annoying fact that this info is not available on all ISP's webpages (e.g. under FAQ or a technical info section) that runs such a practice - you have to beg for it. If you have higher requirements than mainstream web browsing and mail via your ISP's own servers, it is better to check with your potential new ISP before moving your business there and find out later that you have not gotten the connection you need.

If you need to run your own web, SMTP or FTP service over standard ports (running them on unstandard ports are of course no problem), and you have an internet provider that does not think that your internet conection should be fully open and your own responsibility, you could use services like the free DynDNS to get traffic in and out.

References:
Telenor's info on blocking/opening SMTP port 25 (Norwegian)
Get's only info on the subject - not much (Norwegian)

XP Firewall option "My network (subnet) only" blocks traffic from local subnet

Problem: The weirdest problem occurred on a Windows XP Service Pack 3 computer: I changed a firewall rule scope from "Any computer" to "Local subnet only," only to find that the service did not accept traffic from my local subnet anymore. I started investigating, and ended up testing several different services and ports. The same thing happened: Once the port or service had been restrained to the scope "My network only", no traffic from comptuers on the local subnet was allowed through.

Symptoms: I noticed first because I tried to ping the computer. The name was not resolved, because the UDP 137 port (part of the File and Printer sharing entity) for NetBios name resolving blocked when set to "my network only" scope. Same thing happened to the VNC server service - once the 5900 port or the VNC server service was set to "my network only", it was no longer possible to connect to the comptuer from another local host.

Resolution: Sifting through probably a few dozens of webpages left me empty handed. At the end, I decided to rebuild the firewall settings from scratch by clicking the "Restore default settings" button of the advanced tab in Windows Firewall. When I now selected a "Local subnet only" scope, it worked like a charm. My firewall configuration was obviously messed up and needed a reset.

Reason: Who knows?

Apart from understanding what went wrong, the hardest thing in such a situaiton is to know when you should stop wasting time searching for the reason and resort to a tedious rebuild of firewall rules. Most boring: I still do not know what had went wrong, only what solved it. :(

WPF DatePicker: Replace/remove the "Show Calendar" string

Scenario: I am programming in VB.NET using WPF (Windows Presentation Foundation) as the visual platform. The program will among other things also ask the user to select a date. I found and installed the WPF Toolkit from the Microsoft CodePlex website, which includes the DatePicker tool in question.

Problem: This post will probably be obsolete in a few months, but for those of us who needs to use the WPF Toolbox DatePicker tool in its current (April 2009) state in their applications, there's no straightforward way to remove the "Show Calendar" text that shows up on the DatePicker text field when no date is selected. I needed to start out with a blank date - selecting one would be optional for the user.

Solution: On the CodePlex website, they will tell you how to modify the xaml template to achieve just that, but I came up with an (imho) ingenious - or should we say quick and dirty - solution to avoid fiddling with all that. Basically this method consists of two steps:

1. Put a blank Textbox on top of the DatePicker control so that only the date icon shows
2. Add a a couple of code lines to control the transfer of the date between the text box and the date picker.

To acheive no. 1, I had a grid control on my xaml where both the DatePicker and the TextBox are aligned in the same position, e.g. Margins 0 of the grid cell in question.

I found 85 to be just the right length to cover the DatePicker's text field, without hiding its icon. I removed tabstop from the DatePicker to avoid ever landing at the DatePicker's text field that is hidden behind the TextBox, when using the keyboard to navigate in the app. The xaml looks like this:

<my:datepicker height="24" verticalalignment="Top" istabstop="False" textbox="" row="0" column="1" margin="0" name="DatePicker1" horizontalalignment="Left" width="85">

<TextBox Grid.Row="0" Grid.Column="1" Margin="0" Name="TextBox1" HorizontalAlignment="Left" Width="85" />

Now, the only thing needed is a couple of event handlers to transfer the dates back and forth:


Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.Windows.Controls.TextChangedEventArgs) Handles TextBox1.TextChanged

DatePicker1.Text = NormalizeDateString(TextBox1.Text)

End Sub

Private Sub TextBox1_LostFocus(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles TextBox1.LostFocus

TextBox1.Text = DatePicker1.Text

End Sub

Private Sub DatePicker1_SelectedDateChanged(ByVal sender As System.Object, ByVal e As System.Windows.Controls.SelectionChangedEventArgs) Handles DatePicker1.SelectedDateChanged

TextBox1.Focus()

End Sub

Oh, and finally, the NormalizeDateString function referenced above:

Protected Function NormalizeDateString(ByVal DateIn As String) As String

Dim ReturnDato As String
Try

If DateIn.Substring(DateIn.Length - 1) = "." Then DateIn = DateIn.Substring(0, DateIn.Length - 1)
Dim ConvertedDato As DateTime = Convert.ToDateTime(DateIn)
ReturnDato = ConvertedDato.ToShortDateString

Catch ex As Exception

Return ""

End Try

Return ReturnDato

End Function

And voilla! You have a WPF DatePicker that does not display any text if the date is left blank, and that at any time will hold the date the user selected, regardless if he types the date (in the overlaying TextBox) or he selects the date by clicking the DatePicker calendar icon visible to the right of the textbox.