Don’t know how to configure dhclient to persistently look for an IP address lease? We can help you.

Recently we had a customer who came across a DHCP outage. As an aftermath, he lost the system’s IP address.

As part of our Server Management Services, we assist our customers with several DHCP queries.

Today, let us see how we can configure Linux dhclient command to continuously requests an IP lease until DHCP Server/Router grant one.

Configure dhclient to persistently look for an IP address lease

As we mentioned earlier, one of our customers came across a DHCP outage. When the system lost its IP address, to recover it we had to either reboot the system or get a console and restart the network.

Since the dhclient was not running, it was unable to get a new IP address after the DHCP server recovery.

In such a case, Linux dhclient command can provide an IP lease until DHCP Server/Router grants one.

We use the dhclient command to obtain, renew and release a client’s IP address, subnet mask, default gateway, and DNS servers from a DHCP server.

Similarly, we use the ps command to determine if the system is using init or systemd. If PID 1 is init, then we will use the service command.

The dhclient command provides a means for configuring one or more network interfaces using the Dynamic Host Configuration Protocol or BOOTP protocol. However, if these protocols fail, it statically assigns an address.

In order to perform we need to set the PERSISTENT_DHCLIENT option by editing the Ethernet configuration file. It is turned off by default.

Initially, log in as the root user.

Open /etc/sysconfig/network-scripts/ifcfg-eth0 file to set eth0 to persistently look for an IP address lease:

# vi /etc/sysconfig/network-scripts/ifcfg-eth0

At the end configuration, append the line PERSISTENT_DHCLIENT=1:

DEVICE=eth0
ONBOOT=yes
BOOTPROTO=dhcp
PERSISTENT_DHCLIENT=1

Save and close the file.

To test the changes either restart the networking service or reboot the laptop/desktop:

# /etc/init.d/networking restart

Make note that network switches and other protocols may need to configure properly to work with this option.

Furthermore, to display DHCP configuration information:

• Open a command prompt.
• Use ifconfig -a to display all IP configuration information.
• Observe whether we have any network adapters that are DHCP Enabled. If so, identify the DHCP Server, when it shows Lease Obtained and when it shows Lease Expires.

[Need help with the procedure? We’d be happy to assist]

Conclusion

In short, Linux dhclient command can provide an IP lease until DHCP Server/Router grants one. Today, we saw how our Support Techs perform the same.