我使用旧版本的python（2.6）
$ python --version
Python 2.6.6
我想安装模块Fabric 从代理服务器后面安装
$ sudo pip install Fabric==1.13.1 --proxy <proxy>
得到错误
Downloading Fabric-1.13.1-py2-none-any.whl (92kB)
100% |████████████████████████████████| 102kB 141kB/s
Collecting paramiko<3.0,>=1.10 (from Fabric==1.13.1)
Using cached paramiko-2.4.0-py2.py3-none-any.whl
Collecting pyasn1>=0.1.7 (from paramiko<3.0,>=1.10->Fabric==1.13.1)
Using cached pyasn1-0.4.2-py2.py3-none-any.whl
Collecting bcrypt>=3.1.3 (from paramiko<3.0,>=1.10->Fabric==1.13.1)
Using cached bcrypt-3.1.4-cp26-cp26mu-manylinux1_x86_64.whl
Collecting cryptography>=1.5 (from paramiko<3.0,>=1.10->Fabric==1.13.1)
Using cached cryptography-2.1.4.tar.gz
Collecting pynacl>=1.0.1 (from paramiko<3.0,>=1.10->Fabric==1.13.1)
Using cached PyNaCl-1.2.1.tar.gz
Complete output from command python setup.py egg_info:
Download error on https://pypi.python.org/simple/cffi/: [Errno 101] Network is unreachable -- Some packages may not be found!
Couldn't find index page for 'cffi' (maybe misspelled?)
Download error on https://pypi.python.org/simple/: [Errno 101] Network is unreachable -- Some packages may not be found!
No local packages or working download links found for cffi>=1.4.1
以前工作（1年前） 由于遗留问题，我无法升级python。 看起来已被弃用。
需要你的帮助来解决这个问题。