Introduction

Consider a scenario where users behind ISA Server (internal network) start to receive random prompts for authentication while trying to access internet using ISA Server as proxy. The authentication prompt persists even after entering the credentials. To resolve the issue it is necessary to restart Firewall Service.

Although you probably heard or read about this scenario many times, the goal of this post is to give you a compiled version of the action plan and what to look for while analyzing the data.

Data Collection

Start by following the plan from this post (basics section), along with that make sure that binding order is also correct i.e. internal NIC is higher in order then the external. Wrong binding order can cause issues such as the one mentioned here. In addition to the data gathering specified previously, also collect the following data:

1. Use ISA Data Packager while doing repro of the issue.
2. Enable netLogon logging on the ISA server nodes, using command nltest /dbflag:0x2080ffff in the command prompt as per KB109626.
2. Set the Performance counters as specified in this post.

--> The rest is on the blog :

http://blogs.technet.com/b/isablog/archive/2011/01/13/random-authentication-prompts-while-accessing-internet-through-isa-server-followed-by-isa-server-becoming-unresponsive.aspx