How to enable contrib and non-free repositories in Debian

As root you need to edit /etc/apt/sources.lst

Then add contrib and non free at the end of each line that begins with deb and deb-src just like the example:

deb http://http.us.debian.org/debian squeeze main contrib non-free
deb http://security.debian.org squeeze/updates main contrib non-free

Updating SNMP and Downloading All MIBS
To get your missing MIBs perform an apt-get update and follow the instructions below:

% apt-get install snmp-mibs-downloader

Assure that this line is commented out in /etc/snmp/snmp.conf

#mibs :