由于安全限制，我有一个在 Azure 上运行的 Ubuntu 18.04.2 LTS VM，没有公共 IP。我可以使用curl 通过HTTP 下载文件，尽管FTP 不起作用。
这些是我收到的错误：
sudo apt-get update
Err:1 http://mirror.cs.unm.edu/archive bionic InRelease
Connection failed [IP: 64.106.20.76 80]
Err:2 http://mirror.cs.unm.edu/archive bionic-updates InRelease
Connection failed [IP: 64.106.20.76 80]
Err:3 http://mirror.cs.unm.edu/archive bionic-backports InRelease
Connection failed [IP: 64.106.20.76 80]
Err:4 http://mirror.cs.unm.edu/archive bionic-security InRelease
Connection failed [IP: 64.106.20.76 80]
Reading package lists... Done
W: Failed to fetch http://mirror.cs.unm.edu/archive/dists/bionic/InRelease Connection failed [IP: 64.106.20.76 80]
W: Failed to fetch http://mirror.cs.unm.edu/archive/dists/bionic-updates/InRelease Connection failed [IP: 64.106.20.76 80]
W: Failed to fetch http://mirror.cs.unm.edu/archive/dists/bionic-backports/InRelease …