Configuring Secondary Network Cards for A-Series Servers

Additional IP addresses purchased for A-Series servers require proper configuration of secondary network cards to function correctly. This document provides detailed instructions for configuring a secondary network card (eth1) on CentOS 8.4 systems to enable access to additional IPs.

1. Log in to the Server

Access your server using the primary IP address.

2. Check Current Network Configuration

route -n

If the output doesn't show information about eth1, the secondary network card hasn't been properly recognized.

3. Check Network Card Configuration File

Verify if the configuration file for eth1 exists:  vi /etc/sysconfig/network-scripts/ifcfg-eth1

If the file doesn't exist, you'll need to create it manually.

4. Obtain Network Card MAC Address

Run the following command to view all network interface information:  ip address show

Example output:

1: lo:  mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: eth0:  mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether 00:16:3e:00:21:02 brd ff:ff:ff:ff:ff:ff
    inet 172.16.0.231/24 brd 172.16.0.255 scope global dynamic eth0
       valid_lft 315359279sec preferred_lft 315359279sec
    inet6 fe80::216:3eff:fe00:2102/64 scope link
       valid_lft forever preferred_lft forever
3: eth1:  mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether 00:16:3e:00:a8:bf brd ff:ff:ff:ff:ff:ff
    inet 172.16.0.232/24 brd 172.16.0.255 scope global dynamic noprefixroute eth1
       valid_lft 315359279sec preferred_lft 315359279sec
    inet6 fe80::216:3eff:fe00:a8bf/64 scope link
       valid_lft forever preferred_lft forever
4: bond0:  mtu 1500 qdisc noqueue state DOWN group default qlen 1000
link/ether 3e:43:fb:88:2e:e1 brd ff:ff:ff:ff:ff:ff

Locate the MAC address for eth1 in the output (in this example: 00:16:3e:00:a8:bf).

5. Configure Secondary Network Card (eth1)

vi /etc/sysconfig/network-scripts/ifcfg-eth1

Add the following content (replace with your actual MAC address):

DEVICE=eth1
BOOTPROTO=dhcp
ONBOOT=yes
TYPE=Ethernet
USERCTL=yes
PEERDNS=no
IPV6INIT=no
PERSISTENT_DHCLIENT=yes
HWADDR=00:16:3e:00:a8:bf
DEFROUTE=yes

6. Modify Primary Network Card (eth0) Configuration

vi /etc/sysconfig/network-scripts/ifcfg-eth0

Locate  DEFROUTE=yes  and change it to:  DEFROUTE=no

This step ensures the secondary network card can properly handle default routing.

7. Apply Network Configuration

Restart the network service to activate the changes:  sudo systemctl restart NetworkManager