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I would like my isc-dhcp-server instance to listen on my LAN interface only because I'm investigating an issue with my "WiFi router" and configured INTERFACES='p18p1' in /etc/default/isc-dhcp-server where p18p1 is my LAN interface. However, after restart with sudo systemctl restart isc-dhcp-server.service if see

udp        0      0 0.0.0.0:67              0.0.0.0:*                           23088/dhcpd         

in the output of sudo netstat -tupln | grep 67 which leads me to believe that the interfaces configuration value is ignored. Specifying interfaces p18p1; in /etc/dhcpd/dhcpd.conf causes the systemd unit to fail to start - it seems to enforce specification of interfaces in /etc/default/isc-dhcp-server.

I'm using Ubuntu 17.04.

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  • Whats the output of systemctl cat isc-dhcp-server.service? Also if you do sudo /etc/init.d/isc-dhcp-server restart, does it work?
    – heemayl
    Commented May 9, 2017 at 3:16

2 Answers 2

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Try seting the INTERFACE variable in /etc/default/isc-dhcp-server to the desired interface. For example:

INTERFACES="eth2"
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  • didn't work on Ubuntu 20.04 Commented Sep 14, 2021 at 8:23
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Have you tried adding the following to top of the /etc/dhcp/dhcpd.conf file? The syntax might be important:

INTERFACES="p18p1";

This worked for me in Ubuntu Server 18.04 LTS while having multiple active interfaces with different subnets. Assuming no other similar configs exist at the same time anywere else.

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