install centos/rhel kernel-devel and kernel-headers from installation CD

mkdir /media/cdrom
mount /dev/cdrom /media/cdrom

yum --enablerepo=c6-media install kernel-devel-$(uname-r)
yum --enablerepo=c6-media downgrade kernel-headers-$(uname -r)

* downgrade might be helpful when you accidentally installed a newer but mismatch version.