Cannot find a valid baseurl for repo : base problem

Question

I am trying to update yum but with no success. I have tried all existed solution and i cannot fix it This is the error I get

[root@localhost ]# yum update Loaded plugins: fastestmirror, langpacks Loading mirror speeds from cached hostfile Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=stock error was 14: curl#7 - "Failed to connect to 2001:1b48:203::4:10: Network is unreachable"

 One of the configured repositories failed (Unknown),
 and yum doesn't have enough cached data to continue. At this point the only
 safe thing yum can do is fail. There are a few ways to work "fix" this:

     1. Contact the upstream for the repository and get them to fix the problem.

     2. Reconfigure the baseurl/etc. for the repository, to point to a working
        upstream. This is most often useful if you are using a newer
        distribution release than is supported by the repository (and the
        packages for the previous distribution release still work).

     3. Run the command with the repository temporarily disabled
            yum --disablerepo=<repoid> ...

     4. Disable the repository permanently, so yum won't use it by default. Yum
        will then just ignore the repository until you permanently enable it
        again or use --enablerepo for temporary usage:

            yum-config-manager --disable <repoid>
        or
            subscription-manager repos --disable=<repoid>

     5. Configure the failing repository to be skipped, if it is unavailable.
        Note that yum will try to contact the repo. when it runs most commands,
        so will have to try and fail each time (and thus. yum will be be much
        slower). If it is a very temporary problem though, this is often a nice
        compromise:

            yum-config-manager --save --setopt=<repoid>.skip_if_unavailable=true

Cannot find a valid baseurl for repo: base/7/x86_64

At first I did this but I got the same error

[root@localhost ]# ONBOOT=no
[root@localhost ]# dhclient
[root@localhost ]# yum update

Then I went to /etc/yum.repos.d/

vi CentOS-Base.repo

and then I removed # before the baseurl and save it by :x and enter

now I get the following error

[root@localhost yum.repos.d]# yum update
Loaded plugins: fastestmirror, langpacks
Loading mirror speeds from cached hostfile
Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=stock error was
14: curl#7 - "Failed to connect to 2001:1b48:203::4:10: Network is unreachable"
Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=extras&infra=stock error was
14: curl#7 - "Failed to connect to 2001:1b48:203::4:10: Network is unreachable"
Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=updates&infra=stock error was
14: curl#7 - "Failed to connect to 2001:1b48:203::4:10: Network is unreachable"
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
Trying other mirror.
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
Trying other mirror.
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
Trying other mirror.
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
Trying other mirror.
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
Trying other mirror.
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
Trying other mirror.
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
Trying other mirror.
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
Trying other mirror.
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
Trying other mirror.
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
Trying other mirror.


 One of the configured repositories failed (CentOS-7 - Base),
 and yum doesn't have enough cached data to continue. At this point the only
 safe thing yum can do is fail. There are a few ways to work "fix" this:

     1. Contact the upstream for the repository and get them to fix the problem.

     2. Reconfigure the baseurl/etc. for the repository, to point to a working
        upstream. This is most often useful if you are using a newer
        distribution release than is supported by the repository (and the
        packages for the previous distribution release still work).

     3. Run the command with the repository temporarily disabled
            yum --disablerepo=base ...

     4. Disable the repository permanently, so yum won't use it by default. Yum
        will then just ignore the repository until you permanently enable it
        again or use --enablerepo for temporary usage:

            yum-config-manager --disable base
        or
            subscription-manager repos --disable=base

     5. Configure the failing repository to be skipped, if it is unavailable.
        Note that yum will try to contact the repo. when it runs most commands,
        so will have to try and fail each time (and thus. yum will be be much
        slower). If it is a very temporary problem though, this is often a nice
        compromise:

            yum-config-manager --save --setopt=base.skip_if_unavailable=true

failure: repodata/repomd.xml from base: [Errno 256] No more mirrors to try.
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"
http://mirror.centos.org/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] curl#7 - "Failed to connect to 2607:f2d8:1:e::10: Network is unreachable"

I did use the following command too but the error was the same

yum clean all && yum clean metadata && yum clean dbcache && yum makecache && yum update -y

To check for the interent I did the following

[

root@localhost ~]# cat /etc/resolv.conf
; generated by /usr/sbin/dhclient-script
search dhcp.swmed.org
nameserver 199.242.236.1
nameserver 199.242.237.1

then I ping the first one and I recieve the folliwng message

[root@localhost ~]# ping 199.242.236.1
PING 199.242.236.1 (199.242.236.1) 56(84) bytes of data.
64 bytes from 199.242.236.1: icmp_seq=1 ttl=61 time=0.262 ms
64 bytes from 199.242.236.1: icmp_seq=2 ttl=61 time=0.315 ms
64 bytes from 199.242.236.1: icmp_seq=3 ttl=61 time=0.299 ms
64 bytes from 199.242.236.1: icmp_seq=4 ttl=61 time=0.351 ms

/etc?yum.repos.d/CentOS-Base.repo is as follows

# CentOS-Base.repo
#
# The mirror system uses the connecting IP address of the client and the
# update status of each mirror to pick mirrors that are updated to and
# geographically close to the client.  You should use this for CentOS updates
# unless you are manually picking other mirrors.
#
# If the mirrorlist= does not work for you, as a fall back you can try the
# remarked out baseurl= line instead.
#
#

[base]
name=CentOS-$releasever - Base
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os&infra=$infra
baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

#released updates
[updates]
name=CentOS-$releasever - Updates
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates&infra=$infra
baseurl=http://mirror.centos.org/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras&infra=$infra
baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus&infra=$infra
baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0

Answer 1

Set proxy information in the /etc/yum.conf, like this:

proxy=http://xxx.xxx.xxx.xxx:1087
proxy_username=
proxy_password=

Answer 2

I am also facing same issues on CentOS 7.5, After doing all debugging, We found that Hardware Firewall is blocking Yum URLs.

After allowing the urls in firewall my problem has been resolved.