CentOS 8虚拟服务器执行dnf/yum命令时无法解析vault.centos.org主机名的问题求助

大家好，我在CentOS 8的虚拟服务器上执行dnf或yum相关命令时，一直碰到无法解析vault.centos.org主机名的错误，试了自己能想到的方法还是没解决，来这里求助各位大佬！

每次运行命令都会出现类似的报错，比如执行dnf install epel-release时，终端输出如下：

[root@servers03 ~]# dnf install epel-release
AppStream                                          0.0  B/s |   0  B     00:00
Errors during downloading metadata for repository 'appstream':
  - Curl error (6): Couldn't resolve host name for http://vault.centos.org/centos/8/AppStream/x86_64/os/repodata/repomd.xml [Could not resolve host: vault.centos.org]
Error: Failed to download metadata for repo 'appstream': Cannot download repomd.xml: Cannot download repodata/repomd.xml: All mirrors were tried

执行yum update -y时也会报完全一样的错误：

[root@servers03 ~]# yum update -y
CentOS Linux 8 - AppStream                          0.0  B/s |   0  B     00:00
Errors during downloading metadata for repository 'appstream':
  - Curl error (6): Couldn't resolve host name for http://vault.centos.org/centos/8/AppStream/x86_64/os/repodata/repomd.xml [Could not resolve host: vault.centos.org]
Error: Failed to download metadata for repo 'appstream': Cannot download repomd.xml: Cannot download repodata/repomd.xml: All mirrors were tried

我之前查资料，尝试用以下命令修改yum源的配置文件，把镜像列表注释掉并替换baseurl为vault的地址，但执行后问题依然存在：

sed -i 's/mirrorlist/#mirrorlist/g' /etc/yum.repos.d/CentOS-*
sed -i 's|#baseurl=http://mirror.centos.org|baseurl=http://vault.centos.org|g' /etc/yum.repos.d/CentOS-*

现在有点摸不着头脑，不确定是DNS配置的问题，还是源的配置还有其他地方需要调整？希望有遇到过类似问题的朋友能给点解决思路，谢谢大家！

备注：内容来源于stack exchange，提问作者sanja