我的 ubuntu 浏览这个正常无法访问任何站点，apt-get update甚至upgrade出现如下所示的错误，这可能是什么？
sudo apt-get update
Get:1 http://security.ubuntu.com/ubuntu xenial-security InRelease [94,5 kB]
Hit:2 http://ppa.launchpad.net/webupd8team/sublime-text-3/ubuntu xenial InRelease
Err:3 http://br.archive.ubuntu.com/ubuntu xenial InRelease
Cannot initiate the connection to br.archive.ubuntu.com:80 (2801:82:80ff:8000::5). - connect (101: Network is unreachable) [IP: 2801:82:80ff:8000::5 80]
Err:4 http://br.archive.ubuntu.com/ubuntu xenial-updates InRelease
Cannot initiate the connection to br.archive.ubuntu.com:80 (2801:82:80ff:8000::5). - connect (101: Network is unreachable) [IP: 2801:82:80ff:8000::5 80]
Err:5 http://br.archive.ubuntu.com/ubuntu xenial-backports InRelease
Cannot initiate the connection to br.archive.ubuntu.com:80 (2801:82:80ff:8000::5). - connect (101: Network is unreachable) [IP: 2801:82:80ff:8000::5 …