In order to conserve the limited bandwidth available, ISO images are not downloadable from mirror.centos.org

http://us.mirror.nsec.pt/centos/8.1.1911/isos/x86_64/
http://mirror.cogentco.com/pub/linux/centos/8.1.1911/isos/x86_64/
http://repos-va.psychz.net/centos/8.1.1911/isos/x86_64/
http://mirror.centos.iad1.serverforge.org/8.1.1911/isos/x86_64/
http://centos4.zswap.net/8.1.1911/isos/x86_64/
http://mirror.ash.fastserv.com/centos/8.1.1911/isos/x86_64/
http://mirror.cs.vt.edu/pub/CentOS/8.1.1911/isos/x86_64/
http://mirrors.advancedhosters.com/centos/8.1.1911/isos/x86_64/
http://mirror.vtti.vt.edu/centos/8.1.1911/isos/x86_64/
http://repo1.ash.innoscale.net/centos/8.1.1911/isos/x86_64/
http://mirror.vcu.edu/pub/gnu_linux/centos/8.1.1911/isos/x86_64/

http://mirrors.codec-cluster.org/centos/8.1.1911/isos/x86_64/
http://mirror.san.fastserv.com/pub/linux/centos/8.1.1911/isos/x86_64/
http://packages.oit.ncsu.edu/centos/8.1.1911/isos/x86_64/
http://mirror.centos.lax1.serverforge.org/8.1.1911/isos/x86_64/
http://yum.tamu.edu/centos/8.1.1911/isos/x86_64/
http://mirror.atl.genesisadaptive.com/centos/8.1.1911/isos/x86_64/
http://mirrors.xmission.com/centos/8.1.1911/isos/x86_64/
http://ftp.ussg.iu.edu/linux/centos/8.1.1911/isos/x86_64/
http://mirror.nodesdirect.com/centos/8.1.1911/isos/x86_64/
http://mirrors.rcs.alaska.edu/centos/8.1.1911/isos/x86_64/
http://mirror.mojohost.com/centos/8.1.1911/isos/x86_64/
http://repo1.sea.innoscale.net/centos/8.1.1911/isos/x86_64/
http://mirrors.greenmountainaccess.net/centos/8.1.1911/isos/x86_64/
http://mirror.team-cymru.com/CentOS/8.1.1911/isos/x86_64/
http://ftpmirror.your.org/pub/centos/8.1.1911/isos/x86_64/
http://mirror.umd.edu/centos/8.1.1911/isos/x86_64/
http://repos.lax.layerhost.com/centos/8.1.1911/isos/x86_64/
http://mirrors.sonic.net/centos/8.1.1911/isos/x86_64/
http://mirror.steadfastnet.com/centos/8.1.1911/isos/x86_64/
+ others, see the full list of mirrors: https://www.centos.org/download/mirrors/

Mirrors verified Tue Mar 31 10:35:09 2020 UTC

You can also download the ISO images using bittorrent, a peer-to-peer file sharing protocol. The .torrent files can be found from CentOS mirrors. Various bittorrent clients are available, including (in no particular order of preference): utorrent, vuze (Azureus), BitTorrent, Deluge, ctorrent, ktorrent, rtorrent and transmission. Packaged copies of various torrent clients for CentOS can be found in the repositories listed in the following wiki article: https://wiki.centos.org/AdditionalResources/Repositories