When working with KVM virtualization on Fedora/CentOS systems, you'll notice the automatic creation of virbr0 bridge. The common question arises - how to verify which physical or virtual interfaces are actually bridged to it?

The brctl command (from bridge-utils package) provides direct insight:

# Install bridge-utils if missing
sudo yum install bridge-utils   # CentOS/RHEL
sudo dnf install bridge-utils   # Fedora

# Show bridge information
brctl show

Sample output for a KVM setup:

bridge name     bridge id               STP enabled     interfaces
virbr0          8000.525400123456       yes             virbr0-nic

This reveals virbr0-nic as the attached interface, while physical interfaces like en0 would appear here if bridged.

For newer systems using iproute2:

ip link show master virbr0
bridge link show

# Add eth1 to virbr0
sudo brctl addif virbr0 eth1

# Verify addition
brctl show virbr0

If your expected interface doesn't appear:

1. Verify interface exists (ip link show)
2. Check NetworkManager didn't override settings
3. Confirm no conflicting bridge configurations

For permanent changes, edit network scripts:

# CentOS 7 example
/etc/sysconfig/network-scripts/ifcfg-eth1:
BRIDGE=virbr0

When working with virtualization technologies like KVM on Fedora or CentOS, you'll encounter network bridges like virbr0. These bridges act as virtual switches connecting virtual machines to physical network interfaces.
The primary command to inspect bridge configuration is brctl (bridge control):


# Install bridge-utils if needed (older systems)

sudo yum install bridge-utils

# Show all bridges and their members

brctl show


On newer systems using iproute2, you can use:


# List all bridge devices

ip link show type bridge

# Show specific bridge details

bridge link show dev virbr0


When examining KVM's default bridge (virbr0), you might see:


$ brctl show virbr0

bridge name     bridge id               STP enabled     interfaces

virbr0          8000.525400123456       yes             virbr0-nic


The interfaces column shows all attached members. Common scenarios include:

Physical interfaces (eth0, enp3s0)
Virtual interfaces (vnet0, tap0)
Bridge internal interfaces (virbr0-nic)

If your physical interface (en0) isn't showing in bridge members:


# Check current bridge assignment

ip addr show dev en0

# Verify routing table

ip route show


To manually add an interface to a bridge:


# Bring interface down first

sudo ip link set en0 down

# Remove existing IP configuration

sudo ip addr flush dev en0
# Add to bridge

sudo brctl addif virbr0 en0
# Bring interface back up

sudo ip link set en0 up


For CentOS/Fedora, edit network scripts:


# /etc/sysconfig/network-scripts/ifcfg-en0

DEVICE=en0

ONBOOT=yes

BRIDGE=virbr0


Remember to restart networking services after configuration changes.