Configure Bridge and Bonding Devices¶

Overview¶

This guide covers network bridge configuration (for virtualization and container networking) and network bonding/teaming (for redundancy and load balancing) in Linux.

Network Bridges¶

Bridge Concepts¶

A network bridge connects two or more network segments, operating at Layer 2 (Data Link layer). Common uses: - Virtual machine networking - Container networking (Docker, LXC) - Connecting physical and virtual networks - Network segmentation

Key Points: - Bridges forward traffic based on MAC addresses - All bridge members share the same broadcast domain - Bridge itself can have an IP address - Used extensively in virtualization (KVM, VirtualBox, etc.)

Creating Network Bridges¶

Method 1: Using `ip` Command (Temporary)¶

# Create bridge interface
ip link add name br0 type bridge

# Bring bridge up
ip link set br0 up

# Add interfaces to bridge
ip link set eth0 master br0
ip link set eth1 master br0

# Assign IP to bridge
ip addr add 192.168.1.100/24 dev br0

# View bridge
ip link show master br0    # Show bridge members
bridge link show           # Show bridge ports

# Remove interface from bridge
ip link set eth0 nomaster

# Delete bridge
ip link set br0 down
ip link delete br0

Method 2: Using `brctl` Command (Legacy)¶

# Install bridge-utils
dnf install bridge-utils

# Create bridge
brctl addbr br0

# Add interfaces to bridge
brctl addif br0 eth0
brctl addif br0 eth1

# Remove interface
brctl delif br0 eth0

# Show bridge information
brctl show
brctl showmacs br0      # Show MAC addresses
brctl showstp br0       # Show STP info

# Delete bridge
brctl delbr br0

Method 3: NetworkManager (Persistent)¶

# Create bridge connection
nmcli connection add type bridge \
    con-name br0 \
    ifname br0

# Configure bridge IP
nmcli connection modify br0 \
    ipv4.addresses 192.168.1.100/24 \
    ipv4.gateway 192.168.1.1 \
    ipv4.dns 8.8.8.8 \
    ipv4.method manual

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

nmcli connection add type bridge-slave \
    con-name br0-slave-eth1 \
    ifname eth1 \
    master br0

# Activate bridge
nmcli connection up br0
nmcli connection up br0-slave-eth0
nmcli connection up br0-slave-eth1

# View configuration
nmcli connection show br0
nmcli device status

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

# Delete bridge
nmcli connection delete br0
nmcli connection delete br0-slave-eth0

Method 4: Configuration Files (RHEL/CentOS)¶

Bridge interface: /etc/sysconfig/network-scripts/ifcfg-br0

DEVICE=br0
TYPE=Bridge
BOOTPROTO=none
ONBOOT=yes
IPADDR=192.168.1.100
PREFIX=24
GATEWAY=192.168.1.1
DNS1=8.8.8.8
STP=yes
DELAY=0

Bridge member: /etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE=eth0
TYPE=Ethernet
BOOTPROTO=none
ONBOOT=yes
BRIDGE=br0

Restart network:

systemctl restart NetworkManager
# or
nmcli connection reload
nmcli connection up br0

Method 5: Netplan (Ubuntu/Debian)¶

Edit: /etc/netplan/01-netcfg.yaml

network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      dhcp4: no
    eth1:
      dhcp4: no
  bridges:
    br0:
      interfaces:
        - eth0
        - eth1
      dhcp4: no
      addresses:
        - 192.168.1.100/24
      gateway4: 192.168.1.1
      nameservers:
        addresses:
          - 8.8.8.8
          - 8.8.4.4
      parameters:
        stp: true
        forward-delay: 4

Apply:

netplan try
netplan apply

Bridge Management and Monitoring¶

View Bridge Information¶

# Using ip command
ip link show type bridge
bridge link show

# Show FDB (forwarding database)
bridge fdb show
bridge fdb show br br0

# Show VLAN info
bridge vlan show

# Using brctl
brctl show
brctl showmacs br0
brctl showstp br0

Bridge Parameters¶

Spanning Tree Protocol (STP)¶

# Enable/disable STP (prevents loops)
ip link set br0 type bridge stp_state 1  # Enable
ip link set br0 type bridge stp_state 0  # Disable

# Using brctl
brctl stp br0 on
brctl stp br0 off

# Set bridge priority (lower = higher priority)
ip link set br0 type bridge priority 32768
brctl setbridgeprio br0 32768

# Set forward delay
ip link set br0 type bridge forward_delay 1500  # 15 seconds
brctl setfd br0 15

# Set hello time
ip link set br0 type bridge hello_time 200  # 2 seconds
brctl sethello br0 2

# Set max age
ip link set br0 type bridge max_age 2000  # 20 seconds
brctl setmaxage br0 20

# View STP info
bridge -d link show

Port Parameters¶

# Set port priority
bridge link set dev eth0 priority 10

# Set port path cost
bridge link set dev eth0 cost 100

# Disable learning on port
bridge link set dev eth0 learning off

# Disable flooding on port
bridge link set dev eth0 flood off

Network Bonding (Link Aggregation)¶

Bonding Concepts¶

Network bonding (also called NIC teaming) combines multiple network interfaces into a single logical interface for: - Redundancy: Failover if one link fails - Load balancing: Distribute traffic across links - Increased bandwidth: Aggregate throughput (mode-dependent)

Bonding Modes¶

Mode 0 (balance-rr): Round-robin load balancing - Packets transmitted sequentially on each slave - Provides load balancing and fault tolerance - Requires switch support (EtherChannel/LACP)

Mode 1 (active-backup): Active-backup - One slave active, others standby - Provides fault tolerance only - No switch configuration needed - Most compatible

Mode 2 (balance-xor): XOR load balancing - Traffic distributed by source/destination MAC/IP - Provides load balancing and fault tolerance - May require switch configuration

Mode 3 (broadcast): Broadcast - All traffic transmitted on all slaves - Provides fault tolerance - Rarely used

Mode 4 (802.3ad): IEEE 802.3ad LACP - Dynamic link aggregation - Requires switch support for LACP - Provides load balancing and fault tolerance - Recommended for most use cases

Mode 5 (balance-tlb): Adaptive transmit load balancing - Outgoing traffic balanced, incoming on one interface - No switch configuration needed - Provides load balancing and fault tolerance

Mode 6 (balance-alb): Adaptive load balancing - Both TX and RX load balancing - No switch configuration needed - Requires ethtool support

Creating Network Bonds¶

Method 1: Using `ip` Command (Temporary)¶

# Load bonding module
modprobe bonding

# Create bond interface
ip link add bond0 type bond mode active-backup

# Set bonding mode (if not set during creation)
ip link set bond0 type bond mode 802.3ad

# Add slaves
ip link set eth0 master bond0
ip link set eth1 master bond0

# Bring interfaces up
ip link set eth0 up
ip link set eth1 up
ip link set bond0 up

# Assign IP
ip addr add 192.168.1.100/24 dev bond0

# View bond info
cat /proc/net/bonding/bond0
ip link show bond0

# Remove slave
ip link set eth0 nomaster

# Delete bond
ip link set bond0 down
ip link delete bond0

Method 2: NetworkManager (Persistent)¶

# Create bond connection
nmcli connection add type bond \
    con-name bond0 \
    ifname bond0 \
    mode active-backup

# Alternative modes:
# mode balance-rr (0)
# mode active-backup (1)
# mode balance-xor (2)
# mode broadcast (3)
# mode 802.3ad (4)
# mode balance-tlb (5)
# mode balance-alb (6)

# Configure 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

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

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

# Activate
nmcli connection up bond0
nmcli connection up bond0-slave-eth0
nmcli connection up bond0-slave-eth1

# View configuration
nmcli connection show bond0
nmcli device status

# Modify bonding parameters
nmcli connection modify bond0 \
    bond.options "mode=802.3ad,miimon=100,lacp_rate=fast"

# Common bonding options:
# miimon=100               # Link monitoring interval (ms)
# downdelay=200            # Delay before disabling slave
# updelay=200              # Delay before enabling slave
# lacp_rate=fast           # LACP rate (slow/fast)
# xmit_hash_policy=layer3+4  # Hash policy for mode 2/4
# primary=eth0             # Primary interface for mode 1
# arp_interval=250         # ARP monitoring interval
# arp_ip_target=192.168.1.1  # ARP target IP

# Delete bond
nmcli connection delete bond0
nmcli connection delete bond0-slave-eth0
nmcli connection delete bond0-slave-eth1

Method 3: Configuration Files (RHEL/CentOS)¶

Bond interface: /etc/sysconfig/network-scripts/ifcfg-bond0

DEVICE=bond0
TYPE=Bond
BONDING_MASTER=yes
BOOTPROTO=none
ONBOOT=yes
IPADDR=192.168.1.100
PREFIX=24
GATEWAY=192.168.1.1
DNS1=8.8.8.8
BONDING_OPTS="mode=active-backup miimon=100"

Slave interface: /etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE=eth0
TYPE=Ethernet
BOOTPROTO=none
ONBOOT=yes
MASTER=bond0
SLAVE=yes

Slave interface: /etc/sysconfig/network-scripts/ifcfg-eth1

DEVICE=eth1
TYPE=Ethernet
BOOTPROTO=none
ONBOOT=yes
MASTER=bond0
SLAVE=yes

Load bonding module: /etc/modprobe.d/bonding.conf

alias bond0 bonding
options bonding mode=1 miimon=100

Restart network:

systemctl restart NetworkManager

Method 4: Netplan (Ubuntu/Debian)¶

Edit: /etc/netplan/01-netcfg.yaml

network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      dhcp4: no
    eth1:
      dhcp4: no
  bonds:
    bond0:
      interfaces:
        - eth0
        - eth1
      addresses:
        - 192.168.1.100/24
      gateway4: 192.168.1.1
      nameservers:
        addresses:
          - 8.8.8.8
      parameters:
        mode: active-backup
        mii-monitor-interval: 100
        # or for 802.3ad:
        # mode: 802.3ad
        # lacp-rate: fast
        # transmit-hash-policy: layer3+4

Apply:

netplan apply

Bonding Configuration Options¶

Common Bonding Parameters¶

# Bonding modes
mode=0              # balance-rr
mode=1              # active-backup
mode=2              # balance-xor
mode=4              # 802.3ad
mode=5              # balance-tlb
mode=6              # balance-alb

# Link monitoring
miimon=100          # MII link monitoring interval (ms)
arp_interval=250    # ARP monitoring interval (ms)
arp_ip_target=192.168.1.1  # Target for ARP monitoring

# Failover/failback timing
downdelay=200       # Delay before marking slave down (ms)
updelay=200         # Delay before marking slave up (ms)

# Mode-specific options
primary=eth0        # Primary interface (mode 1)
lacp_rate=fast      # LACP heartbeat rate (slow=30s, fast=1s)
xmit_hash_policy=layer3+4  # Hash policy (mode 2/4)
# Options: layer2, layer3+4, layer2+3, encap2+3, encap3+4

# Advanced
fail_over_mac=none  # MAC address handling
all_slaves_active=0 # Deliver packets to all slaves

Set Bonding Options¶

# Using NetworkManager
nmcli connection modify bond0 \
    bond.options "mode=802.3ad,miimon=100,lacp_rate=fast,xmit_hash_policy=layer3+4"

# Using sysfs (temporary)
echo "fast" > /sys/class/net/bond0/bonding/lacp_rate
echo "layer3+4" > /sys/class/net/bond0/bonding/xmit_hash_policy

Monitoring Bonds and Bridges¶

Monitor Bonding Status¶

# View bond status
cat /proc/net/bonding/bond0

# View brief status
ip link show bond0

# Using nmcli
nmcli device show bond0

# Check slave status
cat /sys/class/net/bond0/bonding/slaves
cat /sys/class/net/bond0/bonding/active_slave

# Monitor in real-time
watch -n 1 'cat /proc/net/bonding/bond0'

Monitor Bridge Status¶

# View bridge
bridge link show
ip link show master br0

# View MAC address table
bridge fdb show
bridge fdb show br br0

# View statistics
ip -s link show br0

# Monitor in real-time
watch -n 1 'bridge link show'

Network Teaming (Alternative to Bonding)¶

Teaming vs Bonding¶

teamd: Modern alternative to bonding
More flexible and feature-rich
Better performance monitoring
JSON configuration
Active-backup, load balancing, LACP support

Create Team with NetworkManager¶

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

# Alternative runners:
# "roundrobin"
# "activebackup"
# "loadbalance"
# "broadcast"
# "lacp"

# Configure IP
nmcli connection modify team0 \
    ipv4.addresses 192.168.1.100/24 \
    ipv4.gateway 192.168.1.1 \
    ipv4.method manual

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

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

# Activate
nmcli connection up team0

# View team status
teamdctl team0 state

Team Configuration Examples¶

Active-Backup:

{
    "runner": {
        "name": "activebackup"
    },
    "link_watch": {
        "name": "ethtool"
    }
}

LACP:

{
    "runner": {
        "name": "lacp",
        "active": true,
        "fast_rate": true,
        "tx_hash": ["eth", "ipv4", "ipv6"]
    },
    "link_watch": {
        "name": "ethtool"
    }
}

Load Balance:

{
    "runner": {
        "name": "loadbalance",
        "tx_hash": ["eth", "ipv4", "ipv6"]
    },
    "link_watch": {
        "name": "ethtool"
    }
}

VLAN with Bridges and Bonds¶

Bridge with VLAN¶

# Create VLAN interface
ip link add link eth0 name eth0.100 type vlan id 100

# Add to bridge
ip link set eth0.100 master br0

# Or using NetworkManager
nmcli connection add type vlan \
    con-name vlan100 \
    ifname eth0.100 \
    dev eth0 \
    id 100 \
    master br0

Bond with VLAN¶

# Create VLAN on bond
ip link add link bond0 name bond0.100 type vlan id 100

# Configure VLAN
ip addr add 192.168.100.1/24 dev bond0.100
ip link set bond0.100 up

# Using NetworkManager
nmcli connection add type vlan \
    con-name vlan100 \
    ifname bond0.100 \
    dev bond0 \
    id 100

Troubleshooting¶

Bridge Troubleshooting¶

# Check bridge exists and is up
ip link show br0
brctl show

# Check interfaces in bridge
bridge link show
ip link show master br0

# Check MAC address table
bridge fdb show

# Check STP status
brctl showstp br0

# Verify IP configuration
ip addr show br0

# Check for errors
ip -s link show br0

# Test connectivity
ping -I br0 192.168.1.1

Bond Troubleshooting¶

# Check bond status
cat /proc/net/bonding/bond0

# Verify mode
cat /sys/class/net/bond0/bonding/mode

# Check active slave
cat /sys/class/net/bond0/bonding/active_slave

# Check all slaves
cat /sys/class/net/bond0/bonding/slaves

# Check MII status
cat /sys/class/net/bond0/bonding/mii_status

# View statistics
ip -s link show bond0

# Check slave status individually
ethtool eth0
ethtool eth1

# Test failover (for testing only)
ip link set eth0 down
cat /proc/net/bonding/bond0
ip link set eth0 up

Common Issues¶

Bridge not forwarding traffic:

# Enable forwarding
echo 1 > /proc/sys/net/ipv4/ip_forward

# Check iptables
iptables -L FORWARD

# Disable netfilter on bridge (if needed)
echo 0 > /proc/sys/net/bridge/bridge-nf-call-iptables

Bond slaves not activating:

# Check interfaces are up
ip link set eth0 up
ip link set eth1 up

# Verify no IP on slaves
ip addr flush dev eth0
ip addr flush dev eth1

# Check for conflicting configurations
nmcli connection show

LACP not negotiating:

# Verify switch configuration
# Check LACP is enabled on switch
# Verify correct mode (802.3ad)
cat /proc/net/bonding/bond0 | grep -A 10 "802.3ad"

# Check LACP rate
cat /sys/class/net/bond0/bonding/lacp_rate

Practical Examples¶

Example 1: KVM Bridge¶

# Create bridge for KVM VMs
nmcli connection add type bridge \
    con-name br0 \
    ifname br0 \
    ipv4.method disabled \
    ipv6.method disabled

nmcli connection add type bridge-slave \
    con-name br0-port1 \
    ifname eth0 \
    master br0

nmcli connection up br0

Example 2: Redundant Server Network¶

# Active-backup bond with two NICs
nmcli connection add type bond \
    con-name bond0 \
    ifname bond0 \
    mode active-backup \
    ipv4.addresses 192.168.1.100/24 \
    ipv4.gateway 192.168.1.1 \
    ipv4.method manual

nmcli connection add type ethernet \
    slave-type bond \
    con-name bond0-eth0 \
    ifname eth0 \
    master bond0

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

nmcli connection modify bond0 \
    bond.options "mode=active-backup,miimon=100,primary=eth0"

nmcli connection up bond0

Example 3: LACP Bond for High Bandwidth¶

# 802.3ad LACP bond
nmcli connection add type bond \
    con-name bond0 \
    ifname bond0 \
    mode 802.3ad \
    ipv4.addresses 192.168.1.100/24 \
    ipv4.method manual

nmcli connection modify bond0 \
    bond.options "mode=802.3ad,miimon=100,lacp_rate=fast,xmit_hash_policy=layer3+4"

nmcli connection add type ethernet \
    slave-type bond \
    ifname eth0 \
    master bond0

nmcli connection add type ethernet \
    slave-type bond \
    ifname eth1 \
    master bond0

nmcli connection up bond0

Quick Reference¶

Bridge Commands¶

ip link add br0 type bridge                    # Create bridge
ip link set eth0 master br0                    # Add interface
bridge link show                               # Show bridge ports
brctl show                                     # Show bridges
ip link delete br0                             # Delete bridge

Bond Commands¶

ip link add bond0 type bond mode active-backup # Create bond
ip link set eth0 master bond0                  # Add slave
cat /proc/net/bonding/bond0                    # Show status
ip link delete bond0                           # Delete bond

NetworkManager¶

nmcli connection add type bridge con-name br0 ifname br0
nmcli connection add type bridge-slave ifname eth0 master br0
nmcli connection add type bond con-name bond0 mode active-backup
nmcli connection add type ethernet master bond0 ifname eth0

Exam Tips¶

Know how to create bridges and bonds with NetworkManager
Understand different bonding modes and when to use each
Be familiar with both temporary (ip) and persistent (nmcli/files) configuration
Know how to troubleshoot bond and bridge issues
Understand LACP requirements and configuration
Practice viewing status with /proc/net/bonding/ and bridge commands
Know the difference between bonding and teaming
Understand when bridges are needed (VMs, containers)
Be comfortable with both RHEL and Ubuntu configurations
Know how to verify link status and failover behavior

Configure Bridge and Bonding Devices¶

Overview¶

Network Bridges¶

Bridge Concepts¶

Creating Network Bridges¶

Method 1: Using ip Command (Temporary)¶

Method 2: Using brctl Command (Legacy)¶

Method 3: NetworkManager (Persistent)¶

Method 4: Configuration Files (RHEL/CentOS)¶

Method 5: Netplan (Ubuntu/Debian)¶

Bridge Management and Monitoring¶

View Bridge Information¶

Bridge Parameters¶

Spanning Tree Protocol (STP)¶

Port Parameters¶

Network Bonding (Link Aggregation)¶

Bonding Concepts¶

Bonding Modes¶

Creating Network Bonds¶

Method 1: Using ip Command (Temporary)¶

Method 2: NetworkManager (Persistent)¶

Method 3: Configuration Files (RHEL/CentOS)¶

Method 4: Netplan (Ubuntu/Debian)¶

Bonding Configuration Options¶

Common Bonding Parameters¶

Set Bonding Options¶

Monitoring Bonds and Bridges¶

Monitor Bonding Status¶

Monitor Bridge Status¶

Network Teaming (Alternative to Bonding)¶

Teaming vs Bonding¶

Create Team with NetworkManager¶

Team Configuration Examples¶

VLAN with Bridges and Bonds¶

Bridge with VLAN¶

Bond with VLAN¶

Troubleshooting¶

Bridge Troubleshooting¶

Bond Troubleshooting¶

Common Issues¶

Practical Examples¶

Example 1: KVM Bridge¶

Example 2: Redundant Server Network¶

Example 3: LACP Bond for High Bandwidth¶

Quick Reference¶

Bridge Commands¶

Bond Commands¶

NetworkManager¶

Exam Tips¶

Method 1: Using `ip` Command (Temporary)¶

Method 2: Using `brctl` Command (Legacy)¶

Method 1: Using `ip` Command (Temporary)¶