In CentOS 7, the "Network is unreachable" error can indicate issues with network configuration, including incorrect IP address settings, misconfigured routing tables, or firewall problems. This article provides a detailed guide on diagnosing and resolving this error.

Diagnosing the Problem

Before attempting any fixes, it's crucial to accurately diagnose the root cause of the problem.

• Step 1: Check Network Availability Begin by verifying if the network interface is active using the ip link show command. The output should display the status of your network interface as UP.

• Step 2: Verify IP Address Use the ip addr show command to view assigned IP addresses. Ensure that the IP address is correctly set and assigned to the active network interface.

• Step 3: Check DNS Configuration The /etc/resolv.conf file should contain correct DNS server addresses. Verify that the DNS addresses are correct and accessible.

• Step 4: Inspect Routing Table Use the ip route command to check if the default gateway and routing rules for your network are correctly set.

Resolving the Issue

After diagnosing, you can proceed to fix the identified problems.

• Configure IP Address and Network Parameters If a misconfiguration in the IP address was identified, you can rectify it by modifying the configuration file of your network interface, typically located at /etc/sysconfig/network-scripts/ifcfg-[interface_name]. Here, you can set the correct IP address, subnet mask, default gateway, and DNS servers.

• Fix Routing Table If the issue lies with the routing table, you can use the ip route add default via [gateway_IP_address] command to add the correct default gateway.

• Firewall Configuration If the problem is caused by firewall settings, check the firewall rules and ensure they are not blocking your network traffic. Commands like firewall-cmd --list-all can help display the current firewall rules.

After performing the necessary fixes, restart the network services using the systemctl restart network command and verify that the problem has been resolved. You can do this by attempting to connect to external resources or using the ping command on well-known web servers.

Conclusion

Fixing the "Network is unreachable" error on CentOS 7 requires careful diagnosis and systematic troubleshooting of network issues. Most problems are typically associated with incorrect network configuration settings or firewall blocking. Follow the steps outlined above for effective resolution of this error.