Understanding the Routing Table Information

The routing table in Linux kernel is a crucial component for managing IP packet destinations. Below is a detailed explanation of each column in the routing table:

output item	Explanation
Destination	The target network or host address
Gateway	The gateway (router) address. An asterisk (*) indicates that the destination is on the local network, so no gateway is needed
Genmask	The network mask, which defines the range of IP addresses for which this route applies
Flags	Route flags indicating the type and status of the route (e.g., U for active, H for host on interface)
Metric	The cost metric of the route, which is typically used in routing protocols like RIP or OSPF
Ref	The reference count of the route, which may be used for routing with certain algorithms
Use	The number of active routes using this route
Iface	The interface through which the route is used

Deleting Entries from the Routing Table

To delete an entry from the routing table, you can use the route -n command to view the current routes and then use route del with the appropriate parameters.

Example of Using `route -n` to View Routes

$ route -nKernel IP routing tableDestination     Gateway         Genmask         Flags Metric Ref    Use Iface0.0.0.0         192.168.2.1     0.0.0.0         UG    0      0        0 wlan00.0.0.0         192.168.1.1     0.0.0.0         UG    0      0        0 eth0192.168.1.0     *               255.255.255.0   U     0      0        0 eth0192.168.2.0     *               255.255.255.0   U     0      0        0 wlan0

Deleting Specific Routes

Delete the first route

$ route del -net 0.0.0.0 gw 192.168.2.1 netmask 0.0.0.0 dev wlan0

Delete the second route

$ route del -net 0.0.0.0 gw 192.168.1.1 netmask 0.0.0.0 dev eth0

Delete the third route

$ route del -net 192.168.1.0 gw 0.0.0.0 netmask 255.255.255.0 dev eth0

Delete the fourth route

$ route del -net 192.168.2.0 gw 0.0.0.0 netmask 255.255.255.0 dev wlan0

After running these commands, the routing table should reflect the deletions.

Adding Entries to the Routing Table

To add an entry to the routing table, you can use the route add command with the appropriate parameters. For example, to add a route for the wireless interface:

$ route add-net 192.168.2.0 gw 0.0.0.0 netmask 255.255.255.0 dev wlan0 metric 0

This command adds a route for the network 192.168.2.0 through the wireless interface (wlan0), with the gateway at 0.0.0.0 and a network mask of 255.255.255.0. The metric is set to 0 in this example.

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