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Home / Glossary / PAC
Glossary · Networking

PAC

Proxy Auto Configuration

In plain language

A small file that tells a browser which sites should go through a special gateway and which should go direct.

The metaphor

Like a direction sign at an airport that tells each traveller which gate to use.

Going deeper

How it works

  • The browser fetches the file at start.
  • It contains rules written as a short script.
  • Companies use it to send web traffic through filters.
  • Errors in it can send a user to a dead end.
In practice
  • A company routes web traffic through a filter with one.
  • A staff member cannot reach a site because of a rule.
  • A technician edits the file to add an exception.

A question owners ask

Why would a website not load on the office network?

Sometimes a rule like this sends it to the wrong place. Your IT provider can check.

Related terms
APAccess PointBPDUBridge Protocol Data UnitDHCPDynamic Host Configuration ProtocolDNATDestination Network Address TranslationDNSDomain Name SystemDomain nameDomain registrarDSLDigital Subscriber Line

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