Master Linux ‘route’ Command: Display, Add, Delete, and Persist Routes

Introduction

The route command manipulates the kernel IP routing table. It can display the current routes or add/delete static routes. Routes created from the command line are volatile and disappear after a network‑interface or system reboot unless they are saved (e.g., in /etc/rc.local).

Installation

yum install net-tools

Syntax

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

Common options

-f

: flush all routing entries -p: make the route permanent when used with

add

-n

: numeric output (do not resolve names) -v: verbose output -c: show more information -F: display sent‑packet statistics -C: display route cache

Sub‑commands

add

: add a new route del: delete an existing route -net: destination is a network -host: destination is a host netmask: required when adding a network route gw: specify the gateway (must be reachable) metric: set the route metric (hop count)

Output columns

# 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
10.10.0.0       0.0.0.0         255.255.255.0   !     0      0      0   0
192.168.209.0   0.0.0.0         255.255.255.0   U     100    0      0   ens33

Column meanings:

Destination : target network or host

Gateway : next‑hop address or ‘*’ if none

Genmask : subnet mask (255.255.255.255 for host, 0.0.0.0 for default)

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

Metric : distance to the target (used by routing daemons)

Ref : reference count (unused in Linux kernel)

Use : number of lookups (helps identify cache hits/misses)

Iface : outgoing interface

Examples

Query the routing table

# route -n

Add a static route

# route add -net 10.10.10.0 gw 192.168.209.2 netmask 255.255.255.0 dev ens33

The new entry appears with the UG flag.

Delete a route

# route del -net 10.10.10.0 gw 192.168.209.2 netmask 255.255.255.0 dev ens33

The entry disappears from the table.

Add and remove a reject (blackhole) route

# route add -net 10.10.10.0 netmask 255.255.255.0 reject
# route -n   # shows flag ! for the reject entry
# route del -net 10.10.10.0 netmask 255.255.255.0 reject

The ! flag indicates traffic to that network will be dropped.

Reference

Original tutorial URL: https://www.cnblogs.com/du-z/p/16332641.html