Hi
I had same problem a few days ago.
I think it's an update... maybe a bug.
I solved by edit /etc/sysconfig/dhcpd
and add eth0 there. Mine file looks like:
# Command line options here
DHCPDARGS=eth0
After this, service dhcpd restart solved my problem.
I'm not sure why/how this happen but this solved my problem.
Good luck to you!
Jáder