Network routes in Linux

Network routes on Linux servers are the paths or gateways packets should follow to reach their destinations. Routes can be configured on interface level and system level. Default route also known as default gateway is the IP where packet should discover their path if current network or interface (from which packet originated on server) does not know path for destination IP. This article is about discussing network routes in Linux. It will cover how to define network route for network interface, where and how to define default route or default gateway in Linux etc.

How to check current routes on system?

Current routes on system can be viewed using below commands.

Shell

1 2 3 4 5

# ip route default via 172.31.0.1 dev eth0 172.31.0.0/20 dev eth0  proto kernel  scope link  src 172.31.4.137

Shell

1 2 3 4 5 6 7

# netstat -r Kernel IP routing table Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface default         ip-172-31-0-1.a 0.0.0.0         UG        0 0          0 eth0 172.31.0.0      *               255.255.240.0   U         0 0          0 eth0

Shell

1 2 3 4 5 6 7 8 9

# routel          target            gateway          source    proto    scope    dev tbl         default         172.31.0.1                                     eth0     172.31.0.0/ 20                    172.31.4.137   kernel     link   eth0       127.0.0.0          broadcast       127.0.0.1   kernel     link     lo local      127.0.0.0/ 8            local       127.0.0.1   kernel     host     lo local ----- output clipped -----

You can observe 172.31.0.1 is defined as default gateway on above system.

---

How to configure static route in Linux?

In RHEL : You need to edit below parameters in config file /etc/sysconfig/network-scripts/route-ethX.

Shell

1 2 3 4 5

GATEWAY=10.10.0.1 NETMASK=255.0.0.0 IPADDR=10.10.0.22

where –

• gateway is default gatway for this interface
• netmask is subnet mask value
• IPaddr is IP address of this interface

Caution : Do not change gateways on live production system.

In Debian : You can put your route in file /etc/network/interfaces under intended interface.

Shell

1 2 3 4 5 6 7

auto eth0 iface eth0 inet static       address 10.10.0.22       netmask 255.0.0.0       up route add -net 10.10.0.0 netmask 255.0.0.0 gw 10.10.0.1

In all Linux systems you can use ip route command to define static route. Command syntex is :

# ip route ip-address via dest-address

where, ip-address is IP of host or interface and dest-address is next HOP address i.e. route IP.

---

How to configure default gateway in Linux?

In RHEL : Define default gateway IP against GATEWAY parameter in /etc/sysconfig/network file and then restart network service.

In Debian : Define default gateway IP against gateway parameter in /etc/network/interfaces file and then restart network service.

Or you can try these commands on any Linux (ex gateway as 10.10.0.1).

Shell

1 2 3 4 5

# ip route add default via 10.10.0.1   # route add default gw 10.10.0.1

Once set verify default gateway with commands shown in beginning of this article.

SHARE

sangeethakumar

• 
• 
• 
• 
•