Configuring Static and Persistent Routes in Linux and Dual‑NIC Experiment

This article demonstrates how to configure static routes on a Linux host using the route command, how to make those routes permanent, and how to enable IP forwarding.

Linux routing commands

Add host routes:

route add -host 192.168.1.11 dev eth0
route add -host 192.168.1.12 gw 192.168.1.1

Add network routes:

route add -net 192.168.1.11 netmask 255.255.255.0 eth0
route add -net 192.168.1.0/24 eth0
route add -net 192.168.1.0/24 gw 192.168.1.1

Add default gateway:

route add default gw 192.168.1.1

Delete routes:

route del -host 192.168.1.11 dev eth0
route del default gw 192.168.1.1

Making routes persistent

Four common methods are shown:

Append commands to /etc/rc.local

Set GATEWAY= in /etc/sysconfig/network

Add entries to /etc/sysconfig/static-routes

Enable IP forwarding (temporary: echo "1" > /proc/sys/net/ipv4/ip_forward ; permanent: edit /etc/sysctl.conf and set net.ipv4.ip_forward=1 )

Experiment: dual‑NIC host accessing both internal and external networks

Environment: VMware Workstation Pro, four minimal CentOS 7.3 VMs, Huawei eNSP simulator. The topology includes an external network (10.0.0.0/16), an internal network (172.16.0.0/16), a client with two NICs (10.0.0.101/16 and 172.16.2.101/24), and three internal servers (172.16.2.11, 172.16.3.11, 172.16.4.11). The internal router is configured via eNSP and the following Huawei CLI commands:

<huawei>system-view
[int g0/0/0]
ip address 172.16.2.254 255.255.255.0
[int g0/0/1]
ip address 172.16.3.254 255.255.255.0
[int g0/0/2]
ip address 172.16.4.254 255.255.255.0

Static routes are added on the client to reach the whole internal network:

route add -net 172.16.0.0/16 gw 172.16.2.254

Permanent addition can be placed in /etc/rc.local .

Verification steps include checking the routing table, pinging external sites (e.g., ping www.baidu.com -c 4 ) and internal servers, and accessing HTTP services hosted on the servers via curl . The results show that after adding the single static route, the client can reach both external and all internal subnets.

The article concludes that a single static route solves the dual‑NIC routing problem, while the underlying principles of routing tables and default gateways are explained.