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So I'm trying to set up a DHCP server using isc-dhcp-server on Ubuntu 16.04. Everything seemed to be going fine because I was getting an IP address after shutting down DHCP on my router. Unfortunately as I played with configuration it didn't seem to affect the IP4 address assigned to my Windows 10 machine.

For example after changing the range as shown in the dhcp.conf file to that shown below, the Windows machine would still get 10.0.0.101, which is outside the specified range.

ddns-update-style none;

option domain-name "somename";

default-lease-time 600;

max-lease-time 7200;

authoritative;

log-facility local7;

subnet 10.0.0.0 netmask 255.255.255.0 {

option domain-name-servers 8.8.8.8, 8.8.4.4;

range 10.0.0.60 10.0.0.65;

option routers 10.0.0.1; }

I've tried deleting /var/lib/dhcp/dhcpd.leases & /var/lib/dhcp/dhcpd.leases~ but it made no difference.

I had a little more luck with a Mac. It was assigned an IP address in the range, but after stopping the service:

sudo service isc-dhcp-server stop

I noticed the Mac was still assigned an IP address, albeit a different one:

10.0.0.102.

The windows machine got its 10.0.0.101 IP address as well. The fact that devices are getting an IP address when isc-dhcp-server is stopped got me thinking that I may have multiple DHCP servers running, but how can I tell? (BTW - I wasn't able to find "dhcp-service-identifier" in dhcpd.leases).

I'm not certain that multiple DHCP servers is the problem however because if I understand things correctly, the dhcp.conf file should apply to any DHCP server, so I'm a bit stumped unless:

  1. There's an error in my dhcp.conf file
  2. The DHCP server is running on a different machine (it's not the router!)
  • i thin ipconfig -all in windows would show DHCP server address – meccooll Sep 22 '16 at 8:38
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If you want to know if there are multiple instances running, just check your processes in a terminal window - ps aux | grep dhcpd

To find out if there are more than one dhcp on your network and which IP they might have: on Windows, open a cmd and enter ipconfig /all. The block stating your IP 10.0.0.101 will tell you from which DHCP Server it got its information.

In general, if you want to know on an Ubuntu system where the lease comes from, do grep dhcp /var/log/syslog or if you have a console and your network interface would be eth0, you can do sudo ifdown eth0; sudo ifup -v eth0 in a terminal to see where the configuration info is coming from.

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