Cacheable objects

• HTTP

  • Must have a Last-Modified: tag
  • If origin server required HTTP authentication for request, must have Cache-Control: public tag
  • Ideally also has an Expires or Cache-Control: max-age tag
  • Content provider decides what header tags to include
    • Web servers can auto-generate some tags, such as Last-Modified and Content-Length, under certain conditions

• FTP

  • Squid sets Expires time to fetch timestamp + 2 days

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