Create a cacher for APT with apt-cacher.

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apt-get install apt-cacher

In sources.list:

#repository:
deb http://example.debian.org/debian unstable main contrib non-free 
#becomes:
deb http://repository-cache:3142/example.debian.org/debian unstable main contrib non-free 

Or in apt.conf:

#Use cache:
Acquire::http::Proxy "http://repository-cache:3142/";
#Don't use cache for security.ubuntu.com
Acquire::http::Proxy::security.ubuntu.com "DIRECT";

Check it with:

apt-config dump

Sources:

• http://www.debuntu.org/how-to-set-up-a-repository-cache-with-apt-cacher-p2
• http://www.debian-administration.org/articles/177

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