Viewing the routing table in Linux system is mainly achieved through the ip route and route -n commands. 1. Use ip route show (or ip r) to view the complete routing table, and output key information such as default via (default gateway) and dev (outbound interface); 2. Use route -n is a traditional method, and output includes Destination (target network), Gateway (next hop address), Flags (routing status) and Ife (interface); 3. You can view specific interface routes through ip route show dev [interface name]; 4. Use ip rule show to view policy routing rules, and ip route show table [table number] to view the specified routing table; 5. Temporarily add routes to use ip route add [target network] via [next hop address], but it is invalid after restart. It is recommended to give priority to using ip route, and to handle complex scenarios in combination with ip rule and multi-routing table mechanism.

Viewing the routing table in Linux system is mainly done through the ip command or the traditional route command. If you want to know how the current system forwards network traffic, checking the routing table is the first step and is also very important.

Use the ip route command to view the routing table

This is the most recommended method at present, with clear syntax and more intuitive output.

Execute the command:

 ip route show

Or abbreviated as:

 ip r

Output example:

 default via 192.168.1.1 dev eth0
192.168.1.0/24 dev eth0 scope link

Explain the key parts:

• default via : means the default route, and all traffic that does not match other rules will go to the gateway specified here.
• dev : indicates which network interface to go out.
• scope link : means that this route is only used for local links and does not pass through the gateway.

If you want to only view the routing information of a certain interface, you can add parameters, such as:

 ip route show dev eth0

Use route -n to view routing tables (old method)

Although route command has been gradually replaced, it can still be seen in some old systems.

Execute the command:

 route -n

Output example:

 Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Ifeface
0.0.0.0 192.168.1.1 0.0.0.0 UG 100 0 0 eth0
192.168.1.0 0.0.0.0 255.255.255.0 U 100 0 0 eth0

• Destination : Target network.
• Gateway : Next hop address.
• Flags : U means that the route is available, and G means that the gateway is used.
• Iface : The network interface used.

The -n parameter is added to avoid reverse DNS resolution, so that the output is faster and clearer.

Other practical tips

Sometimes you may want to view more detailed routing information, such as policy routing or multiple routing tables, you can use:

• View all routing tables:

 ip rule show

• View a specific routing table (such as the main routing table numbered 254):

 ip route show table 254

• Add a temporary route (for test):

 ip route add 192.168.2.0/24 via 192.168.1.100

Note: The routes added in this way will fail after restarting. If persistence is required, you need to write to the configuration file, such as configuration in /etc/network/interfaces or NetworkManager .

Basically that's it. Using ip route to view basic routes is enough for daily use, and complex scenarios are combined with ip rule and multi-table mechanism. It is not complicated but easy to ignore that sometimes the routing table is not matched properly. The problem may not be the firewall, but the route itself is not matched.

The above is the detailed content of how to check routing table linux. For more information, please follow other related articles on the PHP Chinese website!