pip install sometimes calls setup.py, which makes it ignore the offline params you specified for pip. To get around that, you need to create a file ~/.pydistutils.cfg
This will create said file:
echo -e '[easy_install]\nallow_hosts = 10.10.120.20\nfind_links = http://10.10.120.20/pypi/simple\nindex-url = http://10.10.120.20/pypi/simple' | tee ~/.pydistutils.cfg
The file looks like this:
[easy_install]
allow_hosts = 10.10.120.20
find_links = http://10.10.120.20/pypi/simple
index-url = http://10.10.120.20/pypi/simple