How to Use the Command 'route' (with examples)

The route command is a powerful tool used for manually modifying the IP routing table in Unix-like operating systems. It allows administrators to manipulate the route table to ensure that the data packets are directed along specific paths through the local network or over the internet. With root privileges, you can add, delete, and lookup specific routes, providing greater control over network traffic. This command is invaluable for network troubleshooting and optimization.

Use Case 1: Add a Route to a Destination Through a Gateway

Code:

sudo route add "destination_ip_address" "gateway_address"

Motivation:
Adding a static route is essential when you want to direct traffic for a specific IP address through a non-default gateway. This might be necessary in complex network environments where multiple gateways are used to optimize the flow of traffic or to route traffic through a specific path for certain services or accessible areas.

Explanation:

• sudo: Grants root privileges, which are necessary to make changes to the routing table.
• route: Invokes the route command.
• add: Command to add a new route.
• "destination_ip_address": The IP address of the host or network you want to route the traffic to.
• "gateway_address": The IP address of the gateway through which the traffic should be directed.

Example Output:

add net destination_ip_address: gateway gateway_address

Use Case 2: Add a Route to a /24 Subnet Through a Gateway

Code:

sudo route add "subnet_ip_address/24" "gateway_address"

Motivation:
Adding a subnet route is crucial when configuring routing for a larger segment of the network. This allows traffic directed at an entire subnet (containing multiple IP addresses) to be routed efficiently through a specified gateway, which can improve network performance and path selection.

Explanation:

• sudo: Ensures the command runs with the necessary administrative privileges.
• route: The command used to manipulate routing tables.
• add: Specifies that a new routing entry is being added.
• "subnet_ip_address/24": Defines the subnet (with a 24-bit subnet mask, typically representing 256 IP addresses) to which this routing rule applies.
• "gateway_address": Denotes the gateway through which the subnet traffic is routed.

Example Output:

add net subnet_ip_address/24: gateway gateway_address

Use Case 3: Run in Test Mode (No Changes, Just Display)

Code:

sudo route -t add "destination_ip_address/24" "gateway_address"

Motivation:
Running the route command in test mode is beneficial for checking your routing commands and configurations before implementing them. This non-destructive approach allows administrators to verify the intended actions of the route modifications without altering the routing table, helping prevent potential network disruptions due to misconfigurations.

Explanation:

• sudo: Runs the command with root access, necessary for potential routing table alterations.
• route: The command tool used.
• -t: Test mode flag; it instructs the command to simulate the routing change without applying it.
• add: Indicates an addition of a route.
• "destination_ip_address/24": Specifies the destination network with a subnet mask.
• "gateway_address": Identifies the intended gateway.

Example Output:

route: writing to routing socket: Network is unreachable
add net destination_ip_address/24: gateway gateway_address (test mode, no change)

Use Case 4: Remove All Routes

Code:

sudo route flush

Motivation:
Flushing the routing table is often needed during significant network reconfigurations or troubleshooting processes. This action removes all entries, resetting the routing table to start fresh, usually during network transitions, configuration corrections, or when troubleshooting persistent network issues.

Explanation:

• sudo: Grants permission to execute administrative tasks.
• route: Accesses the route command tool.
• flush: This parameter removes all route entries, effectively clearing the routing table.

Example Output:

flush routing table

Use Case 5: Delete a Specific Route

Code:

sudo route delete "destination_ip_address/24"

Motivation:
Removing a specific route is crucial when a path is no longer efficient, necessary, or a potential security risk. Route deletion facilitates network optimization and helps maintain security and performance by ensuring that only active, relevant paths are retained.

Explanation:

• sudo: Provides necessary privileges to alter the network routes.
• route: Utilizes the route command tool.
• delete: Command to remove a route entry.
• "destination_ip_address/24": Specifies the exact network or IP route that should be removed.

Example Output:

delete net destination_ip_address/24

Use Case 6: Lookup and Display the Route for a Destination

Code:

sudo route get "destination"

Motivation:
Checking the current route for a particular destination allows network administrators to verify the path and ensure optimal connectivity. It serves as a diagnostic tool to understand how traffic is currently being routed within the network, aiding in troubleshooting and optimization tasks.

Explanation:

• sudo: Grants root access for reading route configurations.
• route: Invokes the route command tool.
• get: Instructs the command to retrieve information about the current route for the specified destination.
• "destination": Could be either a hostname or an IP address, identifying the target destination.

Example Output:

   route to: destination
destination: destination_ip_address
  interface: en0
      flags: <UP,GATEWAY>
 recvpipe  sendpipe  ssthresh  rtt,msec    rttvar  hopcount      mtu     expire
       0         0         0         0         0         0      1500         0 

Conclusion

The route command is an essential utility for managing network traffic direction in Unix-like operating systems. By allowing precise control over routing tables, it empowers network administrators to optimize paths for efficiency, maintain network health and security, and troubleshoot connectivity issues with precision. The examples outlined above illustrate the versatility and power of the route command in various scenarios, demonstrating its importance in network management tasks.