Using the route Command to Display Network Information on Linux

Objective

Learn how to use the route command on Linux to view and manipulate the system’s routing table. This lab focuses on displaying network information, adding and deleting routes, and troubleshooting connectivity issues.

Prerequisites

1. Linux Environment:
   • A Linux system with administrative privileges.
2. Basic Networking Knowledge:
   • Familiarity with IP addresses, gateways, and subnet masks.
3. Installed Tools:
   • Ensure the route command is available:

     route --version
     

   • If not available, install the net-tools package:

     sudo apt update && sudo apt install net-tools
     

Step 1: Viewing the Current Routing Table

1. Open a terminal.
2. Run the route command:

   route
   

3. Analyze the output:
   • Destination: The target network or host.
   • Gateway: The next-hop address used to reach the destination.
   • Genmask: The subnet mask associated with the destination.
   • Iface: The network interface handling the traffic.

   Example Output:

   Kernel IP routing table
   Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
   default         192.168.1.1     0.0.0.0         UG    0      0        0 eth0
   192.168.1.0     *               255.255.255.0   U     0      0        0 eth0
   

   Key Flags:

   • U: Route is up.
   • G: Route is a gateway.
4. Use -n to display numeric addresses:

   route -n
   

   • This avoids resolving hostnames for faster output.

Step 2: Adding a Static Route

1. Add a route to a specific network:

   sudo route add -net <network> netmask <subnet_mask> gw <gateway> dev <interface>
   

   • Replace <network> with the target network (e.g., 192.168.2.0).
   • Replace <subnet_mask> with the subnet mask (e.g., 255.255.255.0).
   • Replace <gateway> with the gateway IP (e.g., 192.168.1.1).
   • Replace <interface> with the network interface (e.g., eth0).

   Example:

   sudo route add -net 192.168.2.0 netmask 255.255.255.0 gw 192.168.1.1 dev eth0
   

2. Verify the new route:

   route -n
   

Step 3: Deleting a Static Route

1. Remove a route:

   sudo route del -net <network> netmask <subnet_mask>
   

   • Example:

     sudo route del -net 192.168.2.0 netmask 255.255.255.0
     

2. Confirm the route has been removed:

   route -n
   

Step 4: Setting the Default Gateway

1. Add or modify the default gateway:

   sudo route add default gw <gateway_ip> dev <interface>
   

   • Replace <gateway_ip> with the IP of the default gateway (e.g., 192.168.1.1).
   • Replace <interface> with the network interface (e.g., eth0).

   Example:

   sudo route add default gw 192.168.1.1 dev eth0
   

2. Verify the default route:

   route -n
   

3. Remove the default gateway if needed:

   sudo route del default gw <gateway_ip>
   

Step 5: Troubleshooting with the Routing Table

1. Check for Missing Routes:
   • Ensure there is a route for the target network in the routing table.
2. Diagnose Gateway Issues:
   • Use ping to verify the gateway is reachable:

     ping <gateway_ip>
     

3. Incorrect Routes:
   • Remove and re-add routes if the traffic is being misrouted.
4. Monitor Route Usage:
   • Use the ip route show command for real-time route information:

     ip route show
     

Additional Tips and Insights

1. Use Persistent Routes:
   • Add routes to the /etc/network/interfaces file or systemd network configuration for persistence across reboots.
2. Combine Tools:
   • Use traceroute or ping alongside route to troubleshoot end-to-end connectivity.
3. Transition to Modern Tools:
   • The route command is deprecated on some distributions. Use ip route for enhanced functionality:

     ip route add <network>/<prefix> via <gateway> dev <interface>
     

4. Security Awareness:
   • Regularly audit routes to ensure no unauthorized changes have been made.

Key Takeaways

1. The route command is essential for viewing and managing routing tables in Linux.
2. Understanding how to add, delete, and troubleshoot routes helps ensure proper network connectivity.
3. Transitioning to modern tools like ip route ensures compatibility with newer Linux distributions.