This post is a revised version of link.

The following steps should be followed:

1. Edit the file /etc/dnsmasq.conf on your router, and update the mac address associated with the intended ip address.

   dhcp-host=<mac address>,<ip address>
   

2. Stop dnsmasq service

   sudo systemctl stop …

Here are the steps for configuring a DHCP server in a local network.

Set static IP to the second network card enp9s3 (this name can be different on a different PC) on the DHCP server PC. Run

 sudo vi /etc/network/interfaces

Edit the file according to this sample:

# interfaces(5) file used by ifup(8) …

Problem

Ethernet RTL8111/8168/8411 is not recognized by kernel 4.4.39-rt50. Running ifconfig shows only the other network interface and lo.

Solution

It turns out the realtime kernel does not have module r8168. Instead it contains r8169. However, by installing r8168-dkms the r8169 module is …