sudo systemctl status isc-dhcp-server.service

● isc-dhcp-server.service - LSB: DHCP server
   Loaded: loaded (/etc/init.d/isc-dhcp-server)
   Active: failed (Result: exit-code) since Fri 2014-12-12 13:19:25 CST; 2min 43s ago
  Process: 1677 ExecStart=/etc/init.d/isc-dhcp-server start (code=exited, status=1/FAILURE)

Dec 12 13:19:23 semplice dhcpd[1684]: you want, please write a subnet declaration
Dec 12 13:19:23 semplice dhcpd[1684]: in your dhcpd.conf file for the network segment
Dec 12 13:19:23 semplice dhcpd[1684]: to which interface eth0 is attached. **
Dec 12 13:19:23 semplice dhcpd[1684]:
Dec 12 13:19:23 semplice dhcpd[1684]:
Dec 12 13:19:25 semplice isc-dhcp-server[1677]: Starting ISC DHCP server: dhcpdcheck syslog for diagnostics. ... failed!
Dec 12 13:19:25 semplice isc-dhcp-server[1677]: failed!
Dec 12 13:19:25 semplice systemd[1]: isc-dhcp-server.service: control process exited, code=exited status=1
Dec 12 13:19:25 semplice systemd[1]: Failed to start LSB: DHCP server.
Dec 12 13:19:25 semplice systemd[1]: Unit isc-dhcp-server.service entered failed state.