Possible DNS issue when using yum: "Could not resolve host: (every mirror); Unknown error" Centos 7

Question

Some specifications and background information: Running Centos Linux release 7.2.1511 (core), Static IP address, Dedicated server machine not configured by me, also I have very little linux experience.

I am trying to set up the server to host a tomcat web application that uses a MySQL database. However whenever I try to install the required software I get a "Could not resolve host error". I have tried multiple suggestions and the solutions in a previous similar question: Could not resolve host. However none seem to work.

I can successfully ping my local host 127.0.0.1, but not googles public nameserver 8.8.8.8. When I try ping 8.8.8.8 and the public-gateway address there is 100% packet loss. Which in the previous question's answer indicates the local network configuration is wrong and you'll have to check the configuration. Below is the local network configuration:

Network information

[xxxx]$ nmcli d
DEVICE  TYPE      STATE      CONNECTION
enp3s0  ethernet  connected  enp3s0
lo      loopback  unmanaged  --

[xxxx]$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000

My etc/resolv.conf file contains

nameserver 8.8.8.8 
nameserver 127.0.0.1

host google.com simply results in: -bash: host: command not found This is also the case with the nslookup and dig commands.

Output:

[xxxx]$ sudo yum update
Loaded plugins: fastestmirror
http://ca.mirror.babylon.network/centos/7.2.1511/os/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: ca.mirror.babylon.network; Unknown error"
Trying other mirror.
http://mirror.netaddicted.ca/CentOS/7.2.1511/os/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: mirror.netaddicted.ca; Unknown error"
Trying other mirror.
etc...

firewall-cmd --list-all

[xxxx]$ firewall-cmd --list-all
public (default, active)
  interfaces: enp3s0
  sources:
  services: dhcpv6-client http https ssh
  ports: 10000/tcp
  masquerade: no
  forward-ports:
  icmp-blocks:
  rich rules:

google's public nameserver ping failure

[xxxx]$ ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
^C
--- 8.8.8.8 ping statistics ---
8 packets transmitted, 0 received, 100% packet loss, time 6999ms

Local gateway ping failure

[xxxx]$ ping xxx.xxx.xx.xxx
...
11 packets transmitted, 0 received, 100% packet loss, time 9999ms

Further specification and update: The server is connected to a larger network managed by an IT department. I am currently contacting one of the IT employees to ensure the firewall is open for this server.

I hope this is relevant and useful information. Thanks in advance for you time. I will update the question once I know if the problem was on the IT staff side and the firewall configuration.

Final Update: This error was in fact due to the firewall configuration. Once the IT staff allowed access there was no longer any issue.

Solution

Check if your firewall is blocking the queries or responses:

sudo firewall-cmd --list-all

You can try to disable de firewall to check for sure if that's the cause:

sudo systemctl stop firewalld

If the firewall is the issue, you should allow the DNS service, allowing TCP/UDP traffic to/from the port 53.

Comments

[Dillon]

Thanks, Leo I suspect it is a firewall issue and am going to contact the IT security department to ensure they are allowing the server access through the firewall while I update the system. The firewall-cmd --list-all command doesn't show anything being blocked so I suspect it is the firewall handled by the University staff which I will just have to wait for them to configure to allow the server access.

[Leo]

You are welcome. It might very well be that. I hope you solve it soon, if you do and found my answer helpful please accept it later. Regards