What are PAC files used for?

Question

Options

• Auser agent-based policies
• Bexplicit forward mode proxy deployments
• Ctransparent mode proxy deployments
• DL4TM

• A
  2% (1)
• B
  89% (56)
• C
  6% (4)
• D
  3% (2)

Explanation

PAC (Proxy Auto-Configuration) files are JavaScript files deployed to clients that instruct browsers and applications which proxy server to use for a given URL - this is inherently an explicit configuration, meaning the client knowingly routes traffic through a proxy. This makes B correct: PAC files are the standard mechanism for explicit forward proxy deployments, where clients are deliberately pointed at a proxy rather than having traffic intercepted transparently.

Why the distractors are wrong:

• A (user agent-based policies): PAC files can reference the user agent string in their logic, but their purpose is proxy selection, not enforcing user agent policies.
• C (transparent mode): Transparent proxies intercept traffic at the network level without any client-side configuration, making PAC files unnecessary and irrelevant.
• D (L4TM): Layer 4 Traffic Management also operates below the application layer, intercepting packets without client awareness - again no PAC file needed.

Memory tip: Think of the "E" in Explicit matching the "E" in PAC filE - when you explicitly tell a client "use this proxy," you hand it a PAC file. Transparent and L4 proxies are invisible to the client, so they need no file at all.

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