A question I see a lot is how can you tell if caching is working on the ISA or TMG firewall. There are a number of ways you can check this. My preferred method is to use the ISA or TMG firewall performance counters. However, there is a potential drawback to using the counters, and that’s the fact that they show historical information for the most part.
A good way to tell if caching is working in real time is to use the ISA or TMG firewall console. Get into the firewall’s logging facility and check the details of the log entries. Here’s are some guidelines:
- In the ISA or TMG firewall console, select the Logging page on the Monitoring node.
- Edit the existing filter to show HTTP traffic only.
- Add the following columns to the log results pane: Object Source and Cache Information. The Object Source column indicates the source that was used to retrieve the current object, and the Cache Information column indicates the reason why an object was or was not cached.
- When a Web request is delivered by cache content, the Object Source for the request will be Cache. How caching is configured determines how many Web requests are delivered from cache instead of from the Internet.
The figures below shows an example.
Thomas W Shinder, M.D., MCSE
Sr. Consultant / Technical Writer