How to Bind Two NICs to a Single IP for High Availability on Linux

To achieve network high availability, multiple NICs can be bonded into a virtual interface (bond) so that a single IP is used and failure of one NIC does not interrupt connections. Linux implements this via the bonding driver (called bonding, etherchannel, or team).

Bonding methods

Two main methods: bond and team. Below we focus on bond.

Supported bonding modes

Bond supports seven modes (0‑6). Commonly used are: mode=0: balance‑load with automatic failover, requires switch configuration. mode=1: active‑backup, no switch config needed. mode=6: balance‑load with failover, no switch config needed. Other modes: mode=2: XOR of MAC addresses, configurable via xmit_hash_policy . mode=3: broadcast to all slaves. mode=4: dynamic link aggregation (requires ethtool support and IEEE 802.3ad switch). mode=5: based on slave speed (requires ethtool support).

Configuration steps

# Load bonding module
modprobe --first-time bonding
lsmod | grep bonding

# Create /etc/sysconfig/network-scripts/ifcfg-bond1
DEVICE=bond1
TYPE=Bond
IPADDR=192.168.171.111
NETMASK=255.255.255.0
GATEWAY=192.168.171.2
DNS1=114.114.114.114
DNS2=8.8.8.8
USERCTL=no
BOOTPROTO=none
ONBOOT=yes

# Configure slave interfaces (ens33, ens36)
# Example for ens33
DEVICE=ens33
TYPE=Ethernet
ONBOOT=yes
BOOTPROTO=none
DEFROUTE=yes
IPV4_FAILURE_FATAL=no
NAME=ens33
MASTER=bond1
SLAVE=yes

# Example for ens36 (similar)

# Load bonding options
echo "alias bond1 bonding
options bonding mode=1 miimon=200" > /etc/modules-load.d/bonding.conf

# Restart network
systemctl restart network

After configuration, the IP address is assigned only to bond1; the physical NICs have no IP. Verify with ip a show bond1 and cat /proc/net/bonding/bond1. If either slave goes down, traffic continues via the other.

Notes

On VMware Workstation, do not use ifdown on the slaves; instead disconnect the network adapter in the VM settings.