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I have 2 web servers load-balanced, trying to access images from a 3rd server using pass-through authentication.

The servers are in a workgroup as my host does not support domains.

No matter what file/IIS permissions I set, the web servers can't get access to the images.

Just what user does an anonymous website run as in IIS 6?

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By default, most ASP.NET functions run under the app pool identity, which, by default, is NETWORK SERVICE. This means that the computername$ account is seen across the network.

Some things run as the website's anonymous user account, which is IUSR_computername, and if you set impersonation="true" then most things will run as the IUSR_computername.

If you can place your site in a dedicated app pool, my recommendation is to create a custom user for your app pool, using passthrough auth as you suggested, with the same user/password. The user must be added to the IIS_WPG group on each server. Then make sure that impersonation is set to false, or isn't set (false by default). Then that user will be used for network access.

It's possible that you will still get Code Access Security (CAS) errors. If so, you'll need to grant the UNC path access using the caspool tool.

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The user IUSR_computername, which is a member of the Guest group. (more here)

If you create a new user with the same username and password on all three systems, and set that as the identity for your app, you should be able to access the files on the backend server without issue.

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