https://www.server-world.info/query?os=CentOS_5&p=dhcp
以下のエラーが出た場合
removing mirrorlist with no valid mirrors: /var/cache/yum/base/mirrorlist.txt
以下サイト参照にて/etc/yum.repos.d/CentOS-Base.repoを修正
http://koredekaiketsu.blogspot.jp/2017/04/linuxyumyumrepo-error.html
[base]
name=CentOS-$releasever - Base
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&rep
o=os
#baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/
baseurl=http://vault.centos.org/5.11/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5

# yum -y install dhcp
# cp -f /usr/share/doc/dhcp*/dhcpd.conf.sample /etc/dhcpd.conf
# vi /etc/dhcpd.conf