NetworkManager Configuration: Advanced Networking in CentOS/RHEL

Tyler Maginnis | February 16, 2024

NetworkManagerCentOSRHELnetworkingnmcliLinux

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NetworkManager Configuration: Advanced Networking in CentOS/RHEL

NetworkManager provides dynamic network configuration and management for CentOS/RHEL systems. This guide covers nmcli usage, connection profiles, and advanced networking configurations.

NetworkManager Fundamentals

Basic NetworkManager Commands

Essential nmcli operations:

# Check NetworkManager status
systemctl status NetworkManager

# List all connections
nmcli connection show

# Show device status
nmcli device status

# Display general status
nmcli general status

# Show radio switches
nmcli radio all

Connection Management

Manage network connections:

# Show active connections
nmcli connection show --active

# Display connection details
nmcli connection show "System eth0"

# Bring connection up
nmcli connection up "System eth0"

# Bring connection down
nmcli connection down "System eth0"

# Delete connection
nmcli connection delete "System eth0"

Ethernet Configuration

Static IP Configuration

Configure static IP addresses:

# Create new connection with static IP
nmcli connection add \
    type ethernet \
    con-name "static-eth0" \
    ifname eth0 \
    ipv4.addresses 192.168.1.100/24 \
    ipv4.gateway 192.168.1.1 \
    ipv4.dns "8.8.8.8,8.8.4.4" \
    ipv4.method manual

# Modify existing connection
nmcli connection modify "System eth0" \
    ipv4.addresses 192.168.1.100/24 \
    ipv4.gateway 192.168.1.1 \
    ipv4.dns "8.8.8.8,8.8.4.4" \
    ipv4.method manual

# Add secondary IP
nmcli connection modify "static-eth0" \
    +ipv4.addresses 192.168.1.101/24

# Configure IPv6
nmcli connection modify "static-eth0" \
    ipv6.addresses 2001:db8::100/64 \
    ipv6.gateway 2001:db8::1 \
    ipv6.method manual

DHCP Configuration

Configure DHCP settings:

# Create DHCP connection
nmcli connection add \
    type ethernet \
    con-name "dhcp-eth0" \
    ifname eth0 \
    ipv4.method auto

# Configure DHCP with custom DNS
nmcli connection modify "dhcp-eth0" \
    ipv4.ignore-auto-dns yes \
    ipv4.dns "1.1.1.1,1.0.0.1"

# Set DHCP hostname
nmcli connection modify "dhcp-eth0" \
    ipv4.dhcp-hostname "myserver" \
    ipv4.dhcp-send-hostname yes

Network Bonding

Create Bond Interface

Configure network bonding for redundancy:

# Create bond master
nmcli connection add \
    type bond \
    con-name bond0 \
    ifname bond0 \
    bond.options "mode=active-backup,miimon=100"

# Add slave interfaces
nmcli connection add \
    type ethernet \
    con-name bond0-slave1 \
    ifname eth0 \
    master bond0

nmcli connection add \
    type ethernet \
    con-name bond0-slave2 \
    ifname eth1 \
    master bond0

# Configure bond IP
nmcli connection modify bond0 \
    ipv4.addresses 192.168.1.100/24 \
    ipv4.gateway 192.168.1.1 \
    ipv4.dns 8.8.8.8 \
    ipv4.method manual

Advanced Bond Options

Configure different bonding modes:

# Mode 0 - Round Robin
nmcli connection modify bond0 \
    bond.options "mode=balance-rr,miimon=100"

# Mode 1 - Active Backup
nmcli connection modify bond0 \
    bond.options "mode=active-backup,miimon=100,primary=eth0"

# Mode 2 - Balance XOR
nmcli connection modify bond0 \
    bond.options "mode=balance-xor,miimon=100,xmit_hash_policy=layer3+4"

# Mode 4 - 802.3ad (LACP)
nmcli connection modify bond0 \
    bond.options "mode=802.3ad,miimon=100,lacp_rate=fast"

# Mode 6 - Balance ALB
nmcli connection modify bond0 \
    bond.options "mode=balance-alb,miimon=100"

VLAN Configuration

Create VLAN Interfaces

Configure VLAN tagging:

# Create VLAN interface
nmcli connection add \
    type vlan \
    con-name vlan100 \
    dev eth0 \
    id 100 \
    ipv4.addresses 192.168.100.1/24 \
    ipv4.method manual

# Create VLAN on bond
nmcli connection add \
    type vlan \
    con-name bond0.200 \
    dev bond0 \
    id 200 \
    ipv4.addresses 192.168.200.1/24 \
    ipv4.method manual

# Configure VLAN priority
nmcli connection modify vlan100 \
    vlan.flags 1 \
    vlan.ingress-priority-map "0:3,1:4" \
    vlan.egress-priority-map "3:0,4:1"

Bridge Configuration

Create Network Bridge

Configure bridge for VMs:

# Create bridge
nmcli connection add \
    type bridge \
    con-name br0 \
    ifname br0 \
    ipv4.addresses 192.168.1.100/24 \
    ipv4.gateway 192.168.1.1 \
    ipv4.dns 8.8.8.8 \
    ipv4.method manual

# Add interface to bridge
nmcli connection add \
    type ethernet \
    con-name br0-slave \
    ifname eth0 \
    master br0

# Configure bridge options
nmcli connection modify br0 \
    bridge.stp yes \
    bridge.priority 32768 \
    bridge.forward-delay 15 \
    bridge.hello-time 2 \
    bridge.max-age 20

Network Teams (Alternative to Bonding)

Configure Network Team

Modern alternative to bonding:

# Create team interface
nmcli connection add \
    type team \
    con-name team0 \
    ifname team0 \
    config '{"runner": {"name": "activebackup"}}'

# Add team slaves
nmcli connection add \
    type ethernet \
    con-name team0-port1 \
    ifname eth0 \
    master team0

nmcli connection add \
    type ethernet \
    con-name team0-port2 \
    ifname eth1 \
    master team0

# Configure team runner options
cat > /tmp/team-config.json <<EOF
{
    "runner": {
        "name": "loadbalance",
        "tx_hash": ["eth", "vlan", "ipv4", "ipv6", "tcp", "udp"]
    },
    "link_watch": {
        "name": "ethtool"
    }
}
EOF

nmcli connection modify team0 \
    team.config "$(cat /tmp/team-config.json)"

Wireless Configuration

WiFi Connection Setup

Configure wireless connections:

# Scan for networks
nmcli device wifi list

# Connect to WiFi
nmcli device wifi connect "SSID" password "password"

# Create WiFi profile
nmcli connection add \
    type wifi \
    con-name "Office-WiFi" \
    ifname wlp3s0 \
    ssid "OfficeNetwork" \
    wifi-sec.key-mgmt wpa-psk \
    wifi-sec.psk "secretpassword"

# Configure enterprise WiFi (802.1X)
nmcli connection add \
    type wifi \
    con-name "Corporate-WiFi" \
    ifname wlp3s0 \
    ssid "CorpNetwork" \
    wifi-sec.key-mgmt wpa-eap \
    802-1x.eap peap \
    802-1x.phase2-auth mschapv2 \
    802-1x.identity "username" \
    802-1x.password "password"

VPN Configuration

OpenVPN Setup

Configure OpenVPN connections:

# Import OpenVPN configuration
nmcli connection import \
    type openvpn \
    file client.ovpn

# Create OpenVPN connection manually
nmcli connection add \
    type vpn \
    con-name "Office-VPN" \
    vpn-type openvpn \
    vpn.data "remote=vpn.example.com,
              port=1194,
              ca=/etc/openvpn/ca.crt,
              cert=/etc/openvpn/client.crt,
              key=/etc/openvpn/client.key,
              cipher=AES-256-CBC,
              comp-lzo=yes"

IPSec/L2TP Configuration

# Configure IPSec VPN
nmcli connection add \
    type vpn \
    con-name "IPSec-VPN" \
    vpn-type l2tp \
    vpn.data "gateway=vpn.example.com,
              ipsec-enabled=yes,
              ipsec-psk=sharedsecret,
              user=vpnuser,
              password-flags=2"

Network Profiles and Dispatcher Scripts

Connection Profiles

Manage multiple network profiles:

# Create location-based profiles
# Office profile
nmcli connection add \
    type ethernet \
    con-name "Office" \
    ifname eth0 \
    ipv4.addresses 10.0.0.100/24 \
    ipv4.gateway 10.0.0.1 \
    ipv4.dns "10.0.0.10,10.0.0.11" \
    ipv4.method manual

# Home profile
nmcli connection add \
    type ethernet \
    con-name "Home" \
    ifname eth0 \
    ipv4.method auto

Dispatcher Scripts

Automate network tasks:

# Create dispatcher script
cat > /etc/NetworkManager/dispatcher.d/30-custom <<'EOF'
#!/bin/bash
# NetworkManager dispatcher script

interface=$1
action=$2

case "$action" in
    up)
        # Actions when interface comes up
        if [[ "$interface" == "eth0" ]]; then
            # Update routing
            ip route add 10.10.0.0/16 via 192.168.1.254
            # Start services
            systemctl start custom-service
        fi
        ;;
    down)
        # Actions when interface goes down
        if [[ "$interface" == "eth0" ]]; then
            systemctl stop custom-service
        fi
        ;;
esac
EOF

chmod +x /etc/NetworkManager/dispatcher.d/30-custom

Performance Tuning

Network Optimization

Optimize network performance:

# Configure connection MTU
nmcli connection modify "System eth0" \
    ethernet.mtu 9000

# Set ring buffer sizes
nmcli connection modify "System eth0" \
    ethtool.ring-rx 4096 \
    ethtool.ring-tx 4096

# Configure offload features
nmcli connection modify "System eth0" \
    ethtool.feature-tso on \
    ethtool.feature-gso on \
    ethtool.feature-gro on

Traffic Control

Implement QoS with tc:

# Create tc qdisc configuration
cat > /etc/NetworkManager/dispatcher.d/40-qos <<'EOF'
#!/bin/bash

interface=$1
action=$2

if [[ "$action" == "up" ]] && [[ "$interface" == "eth0" ]]; then
    # Clear existing qdiscs
    tc qdisc del dev eth0 root 2>/dev/null

    # Add HTB qdisc
    tc qdisc add dev eth0 root handle 1: htb default 30
    tc class add dev eth0 parent 1: classid 1:1 htb rate 1000mbit
    tc class add dev eth0 parent 1:1 classid 1:10 htb rate 500mbit
    tc class add dev eth0 parent 1:1 classid 1:20 htb rate 300mbit
    tc class add dev eth0 parent 1:1 classid 1:30 htb rate 200mbit
fi
EOF

chmod +x /etc/NetworkManager/dispatcher.d/40-qos

Troubleshooting

Diagnostic Commands

Network troubleshooting tools:

# Monitor NetworkManager logs
journalctl -u NetworkManager -f

# Enable debug logging
nmcli general logging level DEBUG domains ALL

# Connection diagnostics
nmcli connection show "System eth0" | grep -E "error|warning"

# Monitor connection changes
nmcli monitor

# Test connectivity
nmcli networking connectivity check

Common Issues Resolution

# Reset NetworkManager
systemctl restart NetworkManager

# Reload connection profiles
nmcli connection reload

# Clear DNS cache
systemctl restart systemd-resolved

# Fix permission issues
restorecon -Rv /etc/NetworkManager/

Security Configuration

802.1X Authentication

Configure port-based authentication:

# Configure 802.1X for wired connection
nmcli connection add \
    type ethernet \
    con-name "Secure-LAN" \
    ifname eth0 \
    802-1x.eap md5 \
    802-1x.identity "user@domain.com" \
    802-1x.password "password" \
    connection.permissions user:john

Firewall Zone Assignment

# Assign connection to firewall zone
nmcli connection modify "System eth0" \
    connection.zone internal

# Configure zone for new connections
nmcli connection add \
    type ethernet \
    con-name "DMZ-eth1" \
    ifname eth1 \
    connection.zone dmz \
    ipv4.method auto

Conclusion

NetworkManager provides powerful and flexible network configuration for CentOS/RHEL systems. Master nmcli commands and configuration options to efficiently manage complex network setups, from basic connectivity to advanced features like bonding, VLANs, and VPNs.