User enters code into TextBox, code gets added to URL (using session) - asp.net

Question

I'm using ASP.net 4.0 VB :)
I am using a session variable to add a user entered code into the url of each page. I can get the code to show up at the end of the page's URL that my textbox is on, but what do I add to every page to make sure that the session stays at the end of every URL that person visits during their session? This is the code from the page that the user enters their user code.
Protected Sub IBTextBoxButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles IBTextBoxButton.Click
Session("IB") = IBTextBox.Text
Dim IB As String = Session("IB")
End Sub
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
ProductID.Value = Request.QueryString("id")
If Session("IB") Is Nothing Then
tab4.Visible = "False"
Else
tab4.Visible = "True"
End If
End Sub
This is what I have in the page load of one of the other pages. What else do I add to make sure that variable is added to the URL of that page?
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim IB As String
IB = Session("IB")
End Sub

Answer 1

string url = Request.Url.ToString();
string newUrl = url + url.Contains("?") ? "&" : "?" + "ib=" + Server.UrlEncode(IBTextBox.Text);
Response.Redirect(newUrl);
return;

Answer 2

The approach I might use would be to create a base page class that all of your pages can inherit. The base page would then inherit the System.Web.UI.Page.
Within your base page class, create a property for IB and also handle the page load event.
In that event, check if the QueryString has the IB parameter in it. If it does, set the property to the value in the parameter.
Private _IB As String
Public Property IB() As String
Get
Return _IB
End Get
Set(ByVal value As String)
_IB = value
End Set
End Property
Public Function GetIB(ByVal url As String) As String
If Not(_IB = String.Empty) Then
If (url.Contains("?")) Then
Return "&IB=" & _IB
Else
Return url & "?IB=" & _IB
End If
Else
Return url
End If
End Function
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If Not (String.IsNullOrEmpty(Request.QueryString("IB"))) Then
_IB = Request.QueryString("IB")
End If
End Sub
Finally in your markup you would need to place something like the following at the end of all of your links:
next page

Answer 3

I threw this code into the Master Page to make sure that every page knows whether or not the Session is there. Thanks for all the help everyone!
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
Handles Me.Load
If Session("IB") Is Nothing Then
IBText.Visible = True
IBTextBox.Visible = True
IBTextBoxButton.Visible = True
Else
IBText.Visible = False
IBTextBox.Visible = False
IBTextBoxButton.Visible = False
lblIB.Visible = True
lblIB.Text = "Welcome, " + Session("First_Name") + " " + Session("Last_Name")
End If
End Sub