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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 |
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.
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
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.
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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