yum -- could not resolve host Trying other mirror ... dhclient

After installing a brand new Oracle Linux 7.6 in Virtual box i just wanted to deploy the relevant oracle rpms using 'yum install' command but i faced below error.

Snippet: yum install -y oracle-database-preinstral.....

    Downloading packages:
No Presto metadata available for ol7_UEKR5
No Presto metadata available for ol7_latest
NetworkManager-adsl-1.12.0-8.e FAILED                                         
https://yum.oracle.com/repo/OracleLinux/OL7/latest/x86_64/getPackage/NetworkManager-adsl-1.12.0-8.el7_6.x86_64.rpm: [Errno 14] curl#6 - "Could not resolve host: yum.oracle.com; Unknown error"
rying other mirror.
     .............................
     ............................
     No more Mirror lists..

To resolve this issue i had to call the 'dhclient', which is explained in brief as below.

The Internet Systems Consortium DHCP Client, dhclient, provides a means for configuring one or more network interfaces using the Dynamic Host Configuration Protocol, BOOTP protocol, or if these protocols fail, by statically assigning an address.

The DHCP protocol allows a host to contact a central server which maintains a list of IP addresses which may be assigned on one or more subnets. A DHCP client may request an address from this pool, and then use it on a temporary basis for communication on network. The DHCP protocol also provides a mechanism whereby a client can learn important details about the network to which it is attached, such as the location of a default router, the location of a name server, and so on.

Finally, it worked fine as below also enabled internet as usual.

root@localhost sf_Stage]# dhclient
rooot@localhost sf_Stage]# yum install -y oracle-database-preinstall-18c.x86_64
Loaded plugins: langpacks, ulninfo
Resolving Dependencies
--> Running transaction check
---> Package oracle-database-preinstall-18c.x86_64 0:1.0-1.el7 will be installed
--> Processing Dependency: ksh for package: oracle-database-preinstall-18c-1.0-1.el7.x86_64
--> Processing Dependency: libaio-devel for package: oracle-database-preinstall-18c-1.0-1.el7.x86_64
--> Running transaction check
---> Package ksh.x86_64 0:20120801-139.0.1.el7 will be installed
---> Package libaio-devel.x86_64 0:0.3.109-13.el7 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

======================================================================================================================================================
 Package                                          Arch                     Version                                 Repository                    Size
======================================================================================================================================================
Installing:
 oracle-database-preinstall-18c                   x86_64                   1.0-1.el7                               ol7_latest                    18 k
Installing for dependencies:
 ksh                                              x86_64                   20120801-139.0.1.el7                    ol7_latest                   883 k
 libaio-devel                                     x86_64                   0.3.109-13.el7                          ol7_latest                    12 k

Transaction Summary
======================================================================================================================================================
Install  1 Package (+2 Dependent packages)

Total download size: 913 k
Installed size: 3.2 M
Downloading packages:
No Presto metadata available for ol7_latest
warning: /var/cache/yum/x86_64/7Server/ol7_latest/packages/libaio-devel-0.3.109-13.el7.x86_64.rpm: Header V3 RSA/SHA256 Signature, key ID ec551f03: NOKEY
Public key for libaio-devel-0.3.109-13.el7.x86_64.rpm is not installed
(1/3): libaio-devel-0.3.109-13.el7.x86_64.rpm                                                                                  |  12 kB  00:00:01   
(2/3): oracle-database-preinstall-18c-1.0-1.el7.x86_64.rpm                                                                     |  18 kB  00:00:00   
(3/3): ksh-20120801-139.0.1.el7.x86_64.rpm                                                                                     | 883 kB  00:00:01   
------------------------------------------------------------------------------------------------------------------------------------------------------
Total                                                                                                                 456 kB/s | 913 kB  00:00:02   
Retrieving key from file:///etc/pki/rpm-gpg/RPM-GPG-KEY-oracle
Importing GPG key 0xEC551F03:
 Userid     : "Oracle OSS group (Open Source Software group) "
 Fingerprint: 4214 4123 fecf c55b 9086 313d 72f9 7b74 ec55 1f03

Thanks.