I encounterred this error when i tried to update my proxmox server
apt-get update
Ign http://download.proxmox.com jessie InRelease
Err http://download.proxmox.com jessie Release.gpg
Unable to connect to download.proxmox.com:http:
Ign http://download.proxmox.com jessie Release
Err http://download.proxmox.com jessie/pve-no-subscription amd64 Packages
Unable to connect to download.proxmox.com:http:
Err http://download.proxmox.com jessie/pve-no-subscription Translation-en_US
Unable to connect to download.proxmox.com:http:
Err http://download.proxmox.com jessie/pve-no-subscription Translation-en
Unable to connect to download.proxmox.com:http:
Ign http://security.debian.org jessie/updates InRelease
Err http://security.debian.org jessie/updates Release.gpg
Cannot initiate the connection to security.debian.org:80 (2401:2500:103:11a::7
apt-get update
Ign http://download.proxmox.com jessie InRelease
Err http://download.proxmox.com jessie Release.gpg
Unable to connect to download.proxmox.com:http:
Ign http://download.proxmox.com jessie Release
Err http://download.proxmox.com jessie/pve-no-subscription amd64 Packages
Unable to connect to download.proxmox.com:http:
Err http://download.proxmox.com jessie/pve-no-subscription Translation-en_US
Unable to connect to download.proxmox.com:http:
Err http://download.proxmox.com jessie/pve-no-subscription Translation-en
Unable to connect to download.proxmox.com:http:
Ign http://security.debian.org jessie/updates InRelease
Err http://security.debian.org jessie/updates Release.gpg
Cannot initiate the connection to security.debian.org:80 (2401:2500:103:11a::7