In ASP.NET Web Forms, which mechanism sends data from one page to another as part of the URL, with a limited maximum size for the data that can be sent?

Introduction / Context:
ASP.NET offers several ways to pass data between pages and requests, including query strings, view state, cookies, and session state. Each approach has different characteristics in terms of size limits, visibility, and security. This question focuses on the mechanism that uses the URL itself to carry data, which is especially common in links, redirects, and simple navigation scenarios.

Given Data / Assumptions:

• We are working with web pages that may navigate to other pages.
• Data needs to be sent alongside the URL to the next page.
• The data size is limited by browser and server URL length constraints.

Concept / Approach:
A query string is the part of a URL that follows a question mark, consisting of key value pairs separated by ampersands. For example, example.com/details.aspx?id=10&mode=edit passes two pieces of information in the URL. Because query strings are visible in the address bar and rely on URL length limits, they are best suited for small pieces of non sensitive data such as identifiers and filter values.

Step-by-Step Solution:
Step 1: When a page needs to pass small parameters to another page, it can construct a URL that includes a query string, such as NextPage.aspx?userId=5. Step 2: The browser sends this full URL to the server when navigating to the target page. Step 3: On the server side, the target page reads values from the Request.QueryString collection in ASP.NET. Step 4: The amount of data that can be placed in the query string is limited by browser and server URL length limits, so large data payloads are not appropriate here. Step 5: Because query string values are visible and easily modified, they should not be used to carry sensitive or security critical information without additional protection.

Verification / Alternative check:
You can verify query string usage by examining the address bar while navigating in a web application that uses filter parameters or identifiers. Developer tools display the full URL of each request, including query string parameters. On the server side, logging Request.RawUrl shows that data is indeed appended to the URL, not stored in hidden fields or cookies.

Why Other Options Are Wrong:
Option A is wrong because cookies store data on the client side and are sent in HTTP headers, not directly appended to the URL. Option B is incorrect because view state is stored as a hidden field within the page form, not in the URL, and is primarily used within a single page across postbacks. Option D is wrong because server session state stores data on the server keyed by a session identifier; it does not send the actual session data through the URL.

Common Pitfalls:
One common pitfall is attempting to store large amounts of data or complex objects in query strings, which can exceed URL length limits and expose internal details. Another issue is failing to validate query string parameters on the server, which can open security vulnerabilities such as parameter tampering. Proper use of query strings involves keeping data small, non sensitive, and validating all incoming values before use.

Final Answer:
The described mechanism is the query string, which sends limited size key value data from one page to another as part of the URL.