Network

There are many ways to set up network in CentOS. In this section, we demonstrate how to use ifconfig and systemd-networkd to setup network in CentOS cluster. Both of them can do same thing, but configuration file for systemd-networkd is simpler.

Before start

First we disable NetworkManager and firewalld. This can reduce unnecessary problems.

systemctl disable NetworkManager --now
systemctl disable firewalld --now

ifconfig

Configuration

Edit network scripts in /etc/sysconfig/network-scripts/ifcfg-<device>, where <device> can be something like enp1s0f1 or eth0.

The following changes are required. For the remaining settings, it’s up to you.

TYPE=Ethernet
BROWSER_ONLY=no
BOOTPROTO=static
DEFROUTE=yes
NAME=<interface name>
IPADDR=10.19.0.1
PREFIX=24
GATEWAY=10.19.0.1
DNS1=8.8.8.8
ONBOOT=yes

For master node, you might not need GATEWAY IP setting.

Note

Make sure all nodes’ IP are distinct.

Activate

Enable and start the system service.

systemctl enable network
systemctl restart network

systemd-networkd

Disable ifconfig network service.

systemctl disable network --now

Configuration

Edit configuration file /etc/systemd/network/<device>.network, where <device> can be something like enp1s0f1 or eth0.

[Match]
Name=<device>

[Network]
Address=10.19.0.1/24
Gateway=10.19.0.1
DNS=8.8.8.8
IPForward=ipv4

For master node, you might not need Gateway IP setting.

For worker node, you don’t need IPForward setting.

Important

The <device> in file name can be anything, but the <device> in configuration file must be the same as network interface name. You can find it using command ip link.

Activate

Enable and start systemd-resolved.

systemctl enable systemd-resolved --now
rm -f /etc/resolv.conf
ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf

Enable and start systemd-networkd.

systemctl enable systemd-networkd --now

NAT

After setting up the network, you might found that worker nodes cannot access internet (only master node can). What you need is to set up NAT service on master node.

Important

Perform following operations on master node only.

nftables

Install nftables.

yum install nftables

Add SNAT (source NAT) rules.

# create table with chains
nft add table nat
nft add chain nat prerouting { type nat hook prerouting priority 0 \; }
nft add chain nat postrouting { type nat hook postrouting priority 100 \; }

# add rule
nft add rule nat postrouting ip saddr 10.19.0.0/24 oif enp1s0f1 snat <public IP>

Make settings become permanent.

systemctl enable nftables --now

# After configuring above rules
nft list ruleset >> /etc/sysconfig/nftables.conf

sysctl

If you already set IPForward in systemd-networkd configuration file, you may skip this step.

Add net.ipv4.ip_forward=1 into /etc/sysctl.conf. Then do

sysctl -p

to reload sysctl settings.

Note

If NAT is not working and libvirtd is enabled, try disabling libvirtd (it uses iptables).