Common Network Commands: Route
Route Command Overview
The route command is a part of the older net-tools package used in Linux systems for viewing and manipulating the IP routing table. It provides information about how packets are routed through the network and allows for the addition, deletion, and modification of routes.
Origin and Development
Historically, the route command has been a primary tool for managing network routing in Linux. However, it has largely been replaced by the ip command from the iproute2 package, which offers more advanced features and capabilities. Despite this, route is still commonly used in many Linux distributions for its simplicity and familiarity.
Basic Functionality
The route command serves several functions:
- Displays the current routing table entries.
- Shows destination networks, gateways, and associated interfaces.
- Allows for the addition, deletion, and modification of routes.
Key Command Syntax
1. Display Routing Table:
```
route -n
```
The -n option prevents DNS lookups for faster output.
2. Add a Static Route:
```
route add -net DESTINATION netmask NETMASK gw GATEWAY dev INTERFACE
```
3. Delete a Route:
```
route del -net DESTINATION netmask NETMASK
```
4. Change a Route:
```
route change -net DESTINATION netmask NETMASK gw GATEWAY
```
5. Display Detailed Route Information:
```
route -n -v
```
The -v option provides verbose output.
Example Usage
To execute the command, simply open a terminal and type:
```
route -n
```
Example Output
When you run route -n, the output might look something like this:
```
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.1.1 0.0.0.0 UG 600 0 0 eth0
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
```
Output Breakdown
1. Destination:
The first column indicates the destination network or IP address.
2. Gateway:
The second column specifies the gateway IP address used to reach the destination.
3. Genmask:
The third column indicates the subnet mask for the destination.
4. Flags:
The fourth column displays flags associated with the route:
- U: Route is up
- G: Route is a gateway
5. Metric:
The fifth column indicates the metric value of the route, influencing the route selection (lower values are preferred).
6. Ref:
The sixth column shows the number of references to the route.
7. Use:
The seventh column indicates the number of times the route has been used.
8. Iface:
The last column specifies the network interface (e.g., eth0) associated with the route.
More Examples
1. Example with Multiple Routes:
```
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.1.1 0.0.0.0 UG 600 0 0 eth0
10.0.0.0 192.168.1.1 255.0.0.0 UG 0 0 0 eth0
172.16.0.0 0.0.0.0 255.240.0.0 U 0 0 0 eth1
```
2. Adding a Static Route:
```
route add -net 192.168.2.0 netmask 255.255.255.0 gw 192.168.1.254 dev eth0
```
3. Deleting a Route:
```
route del -net 10.0.0.0 netmask 255.0.0.0
```
4. Changing a Route:
```
route change -net 192.168.1.0 netmask 255.255.255.0 gw 192.168.1.2
```
5. Displaying Detailed Route Information:
```
route -n -v
```
Usage Scenarios
1. Network Troubleshooting:
Use route to verify routing paths and troubleshoot connectivity issues. If a device cannot be reached, checking the routing table can help identify missing or incorrect routes.
2. Identifying Network Configuration:
Network administrators can use route to verify that routing configurations are correctly set up for their environment.
3. Monitoring Network Paths:
Regularly checking the routing table can help network administrators monitor active routes and identify changes in network topology.
4. Configuring Static Routes:
Network administrators can use route add or route del to manage static routes as needed.
5. Scripting Network Configurations:
Include route commands in shell scripts to automate the configuration and monitoring of routing tables.
Limitations
While the route command is useful, it is worth noting that it does not support some advanced features found in the ip command, such as:
- Multiple routing tables
- Policy-based routing
- Better handling of IPv6
The route command is a fundamental utility for managing and monitoring routing tables in Linux. By providing insights into the routes that network packets take, it is essential for troubleshooting and maintaining network connectivity. Although it has been largely superseded by the ip command, it remains an important tool for system administrators, network engineers, and anyone involved in network management.
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