Yum on Centos 8 - Failed to download metadata for repo 'AppStream'

I'm on a fresh Centos 8 install and have tried to use yum for the first time (on this machine). I get the following for any attempt to install or update anything:

yum update
CentOS-8 - AppStream                            0.0  B/s |   0  B     00:00    
Failed to download metadata for repo 'AppStream'
Error: Failed to download metadata for repo 'AppStream'

Port 80 is open although nmap reports it as closed presumably because I haven't yet installed apache. To be double sure I have added port 80 to firewalld which is confirmed:

firewall-cmd --list-ports
25/tcp 80/tcp

I have tried various advice like yum clean and clearing the yum cache but nothing helps.

This is what is in the dnf.log:

2020-03-30T19:33:01Z INFO --- logging initialized ---
2020-03-30T19:33:01Z DDEBUG timer: config: 4 ms
2020-03-30T19:33:01Z DEBUG Loaded plugins: builddep, changelog, config-manager, copr, debug, debuginfo-install, download, generate_completion_cache, needs-restarting, playground, repoclosure, repodiff, repograph, repomanage, reposync
2020-03-30T19:33:01Z DEBUG DNF version: 4.2.7
2020-03-30T19:33:01Z DDEBUG Command: yum install httpd 
2020-03-30T19:33:01Z DDEBUG Installroot: /
2020-03-30T19:33:01Z DDEBUG Releasever: 8
2020-03-30T19:33:01Z DEBUG cachedir: /var/cache/dnf
2020-03-30T19:33:01Z DDEBUG Base command: install
2020-03-30T19:33:01Z DDEBUG Extra commands: ['install', 'httpd']
2020-03-30T19:33:01Z DEBUG repo: downloading from remote: AppStream
2020-03-30T19:33:02Z DEBUG error: Curl error (6): Couldn't resolve host name for http://mirrorlist.centos.org/?release=8&arch=x86_64&repo=AppStream&infra=stock [Could not resolve host: mirrorlist.centos.org] (http://mirrorlist.centos.org/?release=8&arch=x86_64&repo=AppStream&infra=stock).
2020-03-30T19:33:02Z DEBUG Cannot download 'http://mirrorlist.centos.org/?release=8&arch=x86_64&repo=AppStream&infra=stock': Cannot prepare internal mirrorlist: Curl error (6): Couldn't resolve host name for http://mirrorlist.centos.org/?release=8&arch=x86_64&repo=AppStream&infra=stock [Could not resolve host: mirrorlist.centos.org].
2020-03-30T19:33:02Z ERROR Failed to download metadata for repo 'AppStream'
2020-03-30T19:33:02Z DDEBUG Cleaning up.
2020-03-30T19:33:02Z SUBDEBUG 
Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/dnf/repo.py", line 552, in load
    ret = self._repo.load()
  File "/usr/lib64/python3.6/site-packages/libdnf/repo.py", line 394, in load
    return _repo.Repo_load(self)
RuntimeError: Failed to download metadata for repo 'AppStream'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 65, in main
    return _main(base, args, cli_class, option_parser_class)
  File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 98, in _main
    return cli_run(cli, base)
  File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 114, in cli_run
    cli.run()
  File "/usr/lib/python3.6/site-packages/dnf/cli/cli.py", line 1134, in run
    self._process_demands()
  File "/usr/lib/python3.6/site-packages/dnf/cli/cli.py", line 832, in _process_demands
    load_available_repos=self.demands.available_repos)
  File "/usr/lib/python3.6/site-packages/dnf/base.py", line 406, in fill_sack
    self._add_repo_to_sack(r)
  File "/usr/lib/python3.6/site-packages/dnf/base.py", line 136, in _add_repo_to_sack
    repo.load()
  File "/usr/lib/python3.6/site-packages/dnf/repo.py", line 558, in load
    raise dnf.exceptions.RepoError(str(e))
dnf.exceptions.RepoError: Failed to download metadata for repo 'AppStream'
2020-03-30T19:33:02Z CRITICAL Error: Failed to download metadata for repo 'AppStream'