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Static Routing with Linux

Overview​

Note: The NetFoundry zLAN firewall does not manage static routing. Customers must configure and manage their own routes using standard Linux tools. This guide provides step-by-step instructions for managing static routes with the ip command.

What is a Static Route?​

A static route is a manually configured network route that tells the system how to reach a specific network or IP address using a designated path (gateway). Static routes do not change automatically, and are commonly used when:

  • Connecting to remote networks via a specific gateway
  • Isolating traffic through certain interfaces
  • Working with networks not reachable via the default route

Viewing Existing Routes​

To view the current routing table:

ip route show

Example output:

default via 192.168.1.1 dev eth0 
192.168.1.0/24 dev eth0 proto kernel scope link src 192.168.1.100

Explanation:

  • default via 192.168.1.1 dev eth0: All traffic not matched by more specific rules will go through 192.168.1.1 on eth0.
  • 192.168.1.0/24 dev eth0: Traffic to the 192.168.1.0/24 network is sent directly via the local interface eth0.

Adding a Static Route​

To add a static route:

sudo ip route add <destination> via <gateway> dev <interface>

Examples:

  • Add a route to a remote network: 
    sudo ip route add 10.0.2.0/24 via 192.168.1.1 dev eth0
  • Add a route to a single host: 
    sudo ip route add 203.0.113.50 via 192.168.1.1 dev eth0
  • Use a specific source IP: 
    sudo ip route add 10.10.20.0/24 via 192.168.1.1 dev eth0 src 192.168.1.100

Deleting a Static Route​

To remove a static route:

sudo ip route del <destination> via <gateway> dev <interface>

Or, if there’s only one matching route for that destination:

sudo ip route del <destination>

Making Routes Persistent​

By default, routes added with ip route are not persistent—they are lost after a reboot.

Netplan​

Newer Ubuntu and Debian versions use Netplan for network configuration. To create a persistent static route:

  1. Find your Netplan config file (e.g. /etc/netplan/01-netcfg.yaml)
  2. Edit it to include the static route: 
    network:
      version: 2
      ethernets:
        eth0:
          dhcp4: no
          addresses:
            - 192.168.1.100/24
          gateway4: 192.168.1.1
          routes:
            - to: 10.0.2.0/24
              via: 192.168.1.1
  3. Apply the changes: 
    sudo netplan apply

You can add multiple routes under the routes: list.

Legacy ifupdown​

If your system uses the older /etc/network/interfaces method:

iface eth0 inet static
    address 192.168.1.100
    netmask 255.255.255.0
    gateway 192.168.1.1
    up ip route add 10.0.2.0/24 via 192.168.1.1 dev eth0

Summary of Commands​

ActionCommand Example
View routesip route show
Add route to networksudo ip route add 10.0.2.0/24 via 192.168.1.1 dev eth0
Add route to hostsudo ip route add 203.0.113.50 via 192.168.1.1 dev eth0
Delete a routesudo ip route del 10.0.2.0/24 via 192.168.1.1 dev eth0
Persistent (Ubuntu/Debian)Add route to routes: section in /etc/netplan/*.yaml or use up ip route add ... in /etc/network/interfaces
Persistent (RedHat/CentOS/Rocky/AlmaLinux)Use /etc/sysconfig/network-scripts/route-<interface>

Troubleshooting Tips​

  • Use ip route get <IP> to see which path a packet will take: 
    ip route get 10.0.2.10
  • Check available interfaces: 
    ip link show
  • Confirm that the gateway is reachable: 
    ping <gateway-ip>
  • Use traceroute <ip> to see the path packets are taking: 
    sudo apt install traceroute   # Debian/Ubuntu
    sudo yum install traceroute   # RHEL/CentOS
    traceroute 10.0.2.10