IE fails due to some ISPs distort DNS

Case 1

An Intranet portal website is set as IE’s home page. When users are connected to an external network and launch IE, some ISPs might distort the requests and redirect the Intranet website to their own advertise/search websites. Due to the redirect responses have a 301 Permanent redirect status code, after the users connect to Intranet again, IE still won’t open the Intranet portal, but open the ISPs’, even if you enter the portal URL manually.

Solution:

The ISPs should follow the HTTP protocol standard and return a 302 temporarily redirect status code.

Before the ISPs update the response status code (there might be some commercial considerations), users can let IE “forget” the 301 response by deleting IE cache. IE will query DNS again after re-launching.

In case the issue happens frequently, users can configure IE to delete browsing history on exit.

Below group policy can do the same thing (IE8+)

Policy Allow deleting browsing history on exit

User Configuration\Administrative Templates\Windows Components\Internet Explorer\delete browsing history\

See: https://gpsearch.azurewebsites.net/#7004

Case 2

An enterprise user has below proxy configuration.

The user cannot open any website again, after he launches IE in an external network environment, even if he connects back to Intranet later. The root cause is that some ISPs incorrectly redirect https://webserver/config.pac permanently to their advertise/search websites. IE caches the incorrect proxy configuration responses and fails on executing it. As discussed earlier, the response is cached permanently.

Solution

This issue can be fixed similarly by cleaning up IE cache.

Regards,

Juntao from APGC DSI Team