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If Instance Digests are not provided by the Metalink servers, the Link header fields pertaining to this specification MUST be ignored.

Metalinks contain whole file hashes as described in Section 6, and MUST include SHA-256, as specified in FIPS-180-3.

Alex Rousskov pointed out a project for Squid to implement Duplicate Transfer Detection:

• http://comments.gmane.org/gmane.comp.web.squid.devel/15803^{Image Added}
• http://comments.gmane.org/gmane.comp.web.squid.devel/16335^{Image Added}
• http://www.hpl.hp.com/techreports/2004/HPL-2004-29.pdf^{Image Added}

Per Jessen is working on another project for Squid with a similar goal: http://wiki.jessen.ch/index/How_to_cache_openSUSE_repositories_with_Squid^{Image Added}