Configure Multiple VLANs and IP Addresses on a Single NIC in CentOS/RHEL

In scenarios where a Linux server (CentOS/RHEL) needs to host multiple IP addresses from different VLANs on the same physical NIC, you must first ensure the switch port is configured as a trunk and the required VLANs are created.

Load the 8021q Kernel Module

VLAN tagging on CentOS 7/8 and RHEL 7/8 requires the 8021q kernel module. Verify it is not loaded, then load it:

# lsmod | grep -i 8021q   # no output means not loaded
# modprobe --first-time 8021q
# lsmod | grep -i 8021q   # should show the module

You can view module details with:

# modinfo 8021q

Create VLAN Interfaces

Assume the data‑traffic NIC is ens33. Create VLAN 200 and VLAN 300 on this interface:

# ip link add link ens33 name ens33.200 type vlan id 200
# ip link add link ens33 name ens33.300 type vlan id 300

Bring the new interfaces up:

# ip link set ens33.200 up
# ip link set ens33.300 up

Assign IP Addresses

Allocate IPs from the respective subnets:

# ip address add 172.168.10.51/24 dev ens33.200
# ip address add 172.168.20.51/24 dev ens33.300

At this point the VLAN interfaces work, but the configuration will disappear after a reboot.

Persist Configuration with ifcfg Files

Edit the main NIC configuration to disable automatic IP assignment:

# vim /etc/sysconfig/network-scripts/ifcfg-ens33
TYPE=Ethernet
BOOTPROTO=none
DEVICE=ens33
ONBOOT=yes

Create configuration files for each VLAN:

# vim /etc/sysconfig/network-scripts/ifcfg-ens33.200
DEVICE=ens33.200
BOOTPROTO=none
ONBOOT=yes
IPADDR=172.168.10.51
PREFIX=24
NETWORK=172.168.10.0
VLAN=yes

# vim /etc/sysconfig/network-scripts/ifcfg-ens33.300
DEVICE=ens33.300
BOOTPROTO=none
ONBOOT=yes
IPADDR=172.168.20.51
PREFIX=24
NETWORK=172.168.20.0
VLAN=yes

Restart the network service to apply the changes: # systemctl restart network After the restart, the VLAN interfaces retain their IP addresses and remain operational.