Issues:

Suppose you have 2 network cards and their own gateway. The challenge is that you can only have 1 default gateway. How do we work this out?

Solution:

Type the following command

$ ip route show
default via 192.168.1.254 dev eno0 proto static metric 104
192.168.2.0/24 via 192.168.2.254 dev eno1 proto static metric 103
10.10.1.0/24 via 192.168.2.254 dev eno1 proto static metric 103

That means the default route for traffic is via eno1. All traffic except 192.168.2.0 and 10.10.1.0 will pass through the second gateway. How do we do it?

Set Default Route for all traffic

To set all traffic through the default gateway, do the following

$ ip route add default via 192.168.1.254 dev eno0 proto static metric 104

Set Selected IP Subnet for 2nd Gateway

$ ip route add 192.168.2.0/24 via 192.168.2.254 dev eno1 proto static metric 103
$ ip route add 10.10.1.0/24 via 192.168.2.254 dev eno1 proto static metric 103

Setting the DNS Correctly for each Network Card

If each of the Network Cards requires a different DNS, do make sure you put in the /etc/sysconfig/network-scripts

$ vim /etc/sysconfig/network-scripts/ifcfg-eno0

....
....
DEVICE=eno0
ONBOOT=yes
IPADDR=192.168.1.1
GATEWAY=192.168.1.254
DNS1=192.168.1.252
DNS2=192.168.1.253
NETMASK=255.255.255.0

$ vim /etc/sysconfig/network-scripts/ifcfg-eno1

....
....
DEVICE=eno1
ONBOOT=yes
IPADDR=192.168.2.1
GATEWAY=192.168.2.254
DNS1=192.168.2.252
DNS2=192.168.2.253
NETMASK=255.255.255.0

Deleting Route from Table

ip route delete 192.168.2.0/24 via 192.168.2.254 dev eno1 proto static metric 103

References:

1. Two Default Gateways on One System
2. Linux Set up Routing with IP Command