RHEL 7, 8, 9, 10 – Network Issues

Network issues in Red Hat Enterprise Linux (RHEL) can cause service outages, application failures, storage disconnects, and cluster instability.

This guide provides a systematic, version-aware approach to diagnosing and fixing network problems across RHEL 7 through RHEL 10.

1. Identify the Network Problem
Start by identifying what exactly is failing.
Symptom                                            Possible Cause
No network connectivity                      → Interface down, cable, driver
Cannot reach gateway                           → Routing issue
DNS not resolving                                  → DNS configuration
Network slow                                           → Duplex / MTU / congestion
Interface missing                                     → Driver or udev issue
Network fails after reboot                   → NetworkManager config
Services unreachable                             → Firewall or SELinux

2. Check Network Interface Status
List Interfaces
# ip link show
Check Interface IP
# ip addr show
Bring Interface Up
# ip link set eth0 up

3. Verify Network Services (RHEL Differences)
RHEL Version                        Network Service
RHEL 7                                → NetworkManager / network
RHEL 8+                              → NetworkManager only
Check NetworkManager
# systemctl status NetworkManager
Restart if needed:
# systemctl restart NetworkManager

4. Test Basic Connectivity
Test Loopback
# ping 127.0.0.1
Test Gateway
# ping <gateway-ip>
Test External IP
# ping 8.8.8.8
If IP works but hostname fails → DNS issue.

5. Check Routing Table
# ip route show
Ensure a default route exists:
default via <gateway> dev eth0
Add route (temporary):
# ip route add default via <gateway>

6. DNS Troubleshooting
Check DNS Configuration
# cat /etc/resolv.conf
Test DNS Resolution
# nslookup google.com
# dig google.com
NetworkManager DNS
# nmcli dev show | grep DNS

7. NetworkManager (nmcli) Troubleshooting
Show Connections
# nmcli connection show
Check Active Connection
# nmcli device status
Restart Connection
# nmcli connection down <conn-name>
# nmcli connection up <conn-name>

8. Fix Network Issues After Reboot
Check auto-connect:
# nmcli connection show <conn-name> | grep autoconnect
Enable:
# nmcli connection modify <conn-name> connection.autoconnect yes

9. Firewall Issues (firewalld)
Check Firewall Status
# firewall-cmd --state
List Rules
# firewall-cmd --list-all
Allow Service or Port
# firewall-cmd --add-service=ssh --permanent
# firewall-cmd --add-port=8080/tcp --permanent
# firewall-cmd --reload

10. SELinux Network-Related Issues
SELinux can block network connections.
Check SELinux Status
# getenforce
Identify Denials
# ausearch -m avc -ts recent
Enable Required Boolean
# setsebool -P httpd_can_network_connect on

11. Interface Missing or Renamed
List NICs
# lspci | grep -i ethernet
Check Drivers
# lsmod | grep <driver>
Predictable Interface Names
# ip link
Example: ens192 instead of eth0

12. MTU and Performance Issues
Check MTU
# ip link show eth0
Set MTU (Temporary)
# ip link set dev eth0 mtu 9000
Make Permanent
# nmcli connection modify <conn-name> 802-3-ethernet.mtu 9000

13. Bonding / Teaming Issues
Check Bond Status
# cat /proc/net/bonding/bond0
Restart Bond
# nmcli connection down bond0
# nmcli connection up bond0

14. Network Logs and Debugging
Kernel Messages
# dmesg | grep -i network
NetworkManager Logs
# journalctl -u NetworkManager

15. Network Storage Impact (NFS / iSCSI)
Network failures may affect storage mounts.
# showmount -e server_ip
# iscsiadm -m session

16. Best Practices to Prevent Network Issues

• Use NetworkManager consistently
• Validate firewall rules
• Document static IP settings
• Monitor network latency
• Test changes before reboot
• Keep NIC drivers updated

Conclusion
Network troubleshooting in RHEL 7, 8, 9, and 10 follows the same fundamentals:

• Verify interfaces and IPs
• Check routing and DNS
• Validate NetworkManager
• Review firewall and SELinux

Using this step-by-step approach ensures quick resolution and stable connectivity in enterprise Linux environments.