Tag Archives: DHCP

Here’s an example of installing isc-dhcp-server in Ubuntu Server.

Continue reading “Installing and configuring isc-dhcp-server in Ubuntu”

I noticed once in the syslog:

dhcpd self-test failed. Please fix the config file

Isc-dhcp-server was installed on the server.

To check the correctness of the configuration file, use the command:

dhcpd -t
dhcpd -t -cf /dir/dhcpd.conf
/usr/sbin/dhcpd -t

The command should tell which line the error is, but noted that if it is not critical, it may not.
The key “t” executes the configuration test, and “cf” allows you to specify the path to the configuration file if it is not standard.

In my case, in the configuration file /etc/dhcp/dhcpd.conf, someone made a typo, in the line below (there was an extra letter):

authorivtative;

Because of this, an error occurred, but despite the error dhcp worked.
Although there were also some critical errors, such as an incorrectly written mac address, DHCP did not start because of this error.

dhcping – a utility for checking DHCP-servers using unicast packages.

In Ubuntu, you can install dhcping with the command:

sudo apt-get install dhcping

First let’s see what IP-addresses are received and from which gateway:

ifconfig
route
netstat -rn | grep default

Also you can see the information received from DHCP in the directory /var/lib/dhcp/.

In my case, IP is received from the DHCP server 10.0.2.2.
Here’s an example of running dhcping:

dhcping -s 10.0.2.2

If the DHCP server responds, the following information will be displayed:

Got answer from: 10.0.2.2

If there is no answer:

no answer

I’ll describe the dhcping startup keys:
-v (detailed mode)
-V (very detailed mode)
-i (use DHCPINFORM packets)
-r (use DHCPREQUEST packets (standard))
-q (quiet mode)
-t maxwait (response timeout, standard 3 seconds)
-c IP (request the specified IP)
-s IP (send request to specified IP)
-h MAC (use the specified MAC address in the request)
-g IP (use the specified IP gateway in the packet)