ViewState Chunking in asp.net

When the ViewState in your page becomes very large it can be a problem since some firewalls and proxies will prevent access to pages containing huge ViewState sizes. For this purpose ASP.NET introduces the ViewState Chunking mechanism. So ASP.NET enables splitting of the ViewState's single hidden field into several using the MaxPageStateFieldLength property in the web.config section.

When the MaxPageStateFieldLength property is set to a positive number, the view state sent to the client browser is broken into multiple hidden fields.

Setting the MaxPageStateFieldLength property to a negative number (the default) indicates that the view-state field should not be separated into chunks. Setting the MaxPageStateFieldLength to a small number may result in poor performance.

Sample ViewState before:

<input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE"value="/wEPDwUKLTk2Njk3OTQxNg9kFgICAw9kFgICCQ88KwANAGQYAQUJR3JpZFZpZXcxD2dk4sjERFfnDXV/hMFGAL10HQUnZbk=" />

Then set in web.config:

<pages maxPageStateFieldLength="40">

Sample ViewState After :

<input type="hidden" name="__VIEWSTATEFIELDCOUNT" id="__VIEWSTATEFIELDCOUNT"value="3" /><input type="hidden" name="__VIEWSTATE"id="__VIEWSTATE" value="/wEPDwUKLTk2Njk3OTQxNg9kFgICAw9kFgICCQ88" /><input type="hidden" name="__VIEWSTATE1"id="__VIEWSTATE1" value="KwANAGQYAQUJR3JpZFZpZXcxD2dk4sjERFfnDXV/" /><input type="hidden" name="__VIEWSTATE2"id="__VIEWSTATE2" value="hMFGAL10HQUnZbk=" /> 

hope it help you!

From What's New in ASP.NET State Management - MSDN

If the amount of view-state data becomes too large, view-state chunking will automatically split the data into chunks and put the data into multiple hidden-form fields.

Why do we need Viewstate Chunking?

Here is an exerpt from ViewState Overivew - MSDN

Another important consideration is that if the amount of data in a hidden field becomes large, some proxies and firewalls will prevent access to the page that contains them. Because the maximum amount can vary with different firewall and proxy implementations, large hidden fields can cause sporadic problems. To help avoid this problem, if the amount of data stored in the ViewState property exceeds the value specified in the page's MaxPageStateFieldLength property, the page splits view state into multiple hidden fields to reduce the size of each individual field below the size that firewalls reject.