Master the Linux route Command: Manage IP Routing Tables Like a Pro

Overview

The route utility displays and manipulates the kernel IP routing table, allowing you to add static routes after configuring interfaces with ifconfig. Without options it shows the current table; with add or del it modifies the table.

Installation

yum install net-tools

Command Syntax

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

Common flags: -c – show more information -n – do not resolve names -v – verbose processing details -F – display sent packets -C – display route cache -f – flush all routing entries -p – make the route permanent when used with add Key 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 Fields Explanation

The kernel routing table is displayed in columns:

Destination – target network or host

Gateway – gateway address or ‘*’ if none

Genmask – subnet mask (e.g., 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 (usually hop count)

Ref – reference count (unused in Linux kernel)

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

Iface – outgoing interface for the route

Persistence

Routes added directly on the command line disappear after a network‑interface or system reboot. To make them permanent, place the route commands in /etc/rc.local or use the -p flag where supported.

Examples

Query the routing table: route -n Add a static network route:

route add -net 10.10.10.0 gw 192.168.209.2 netmask 255.255.255.0 dev ens33

Verify the addition: route -n Delete the previously added route:

route del -net 10.10.10.0 gw 192.168.209.2 netmask 255.255.255.0 dev ens33

Add a reject (blackhole) route and then remove it:

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