Master Linux Routing: View, Add, and Delete Routes with the route Command

Introduction

route – show/manipulate the IP routing table.

It operates on the kernel's IP routing table, mainly used to create static routes to specific hosts or networks after configuring interfaces with ifconfig.

Using add or del options modifies the table; without them, route simply displays the current contents.

Adding a route directly from the command line is not permanent; the route disappears after a network‑interface or system reboot. To make it persistent, place the route command in /etc/rc.local.

Installation

yum install net-tools

Usage

route [-f] [-p] [Command [Destination] [mask Netmask] [Gateway] [metric Metric]] [if Interface]

-c   Show more information
-n   Do not resolve names
-v   Verbose output
-F   Show sent information
-C   Show route cache
-f   Flush all routing entries
-p   Make the route permanent when used with add

add   : add a new route
 del   : delete a route
 -net  : destination is a network
 -host : destination is a host
 netmask : required when adding a network route
 gw      : gateway through which packets are sent (must be reachable)
 metric  : set route metric (hop count)

Output

[root@master ~]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.209.2   0.0.0.0         UG    100    0      0     ens33
10.10.10.0      -               255.255.255.0   !     0      -      0     -
192.168.209.0   0.0.0.0         255.255.255.0   U     100    0      0     ens33

Explanation of columns:

Destination : target network or host.

Gateway : gateway address or ‘*’ if none.

Genmask : subnet mask; 255.255.255.255 for host, 0.0.0.0 for default route.

Flags : U (up), H (host), G (gateway), R (reinstate dynamic), D (daemon), M (modified), A (addrconf), C (cache), ! (reject).

Metric : distance to target (usually hop count).

Ref : reference count (not used in Linux kernel).

Use : number of lookups (used with -F and -C to show cache misses/hits).

Iface : interface used to send packets.

Examples

Query route

[root@master ~]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref Use Iface
0.0.0.0         192.168.209.2   0.0.0.0         UG    100    0   0   ens33
192.168.209.0   0.0.0.0         255.255.255.0   U     100    0   0   ens33

Add route

[root@master ~]# route add -net 10.10.10.0 gw 192.168.209.2 netmask 255.255.255.0 dev ens33
[root@master ~]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref Use Iface
0.0.0.0         192.168.209.2   0.0.0.0         UG    100    0   0   ens33
10.10.10.0      192.168.209.2   255.255.255.0   UG    0      0   0   ens33
192.168.209.0   0.0.0.0         255.255.255.0   U     100    0   0   ens33

Delete route

[root@master ~]# route del -net 10.10.10.0 gw 192.168.209.2 netmask 255.255.255.0 dev ens33
[root@master ~]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref Use Iface
0.0.0.0         192.168.209.2   0.0.0.0         UG    100    0   0   ens33
192.168.209.0   0.0.0.0         255.255.255.0   U     100    0   0   ens33

Add reject route and delete

[root@master ~]# route add -net 10.10.10.0 netmask 255.255.255.0 reject
[root@master ~]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref Use Iface
0.0.0.0         192.168.209.2   0.0.0.0         UG    100    0   0   ens33
10.10.10.0      -               255.255.255.0   !     0      -   0   -
192.168.209.0   0.0.0.0         255.255.255.0   U     100    0   0   ens33
[root@master ~]# route del -net 10.10.10.0 netmask 255.255.255.0 reject
[root@master ~]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref Use Iface
0.0.0.0         192.168.209.2   0.0.0.0         UG    100    0   0   ens33
192.168.209.0   0.0.0.0         255.255.255.0   U     100    0   0   ens33