# ifconfig re0 172.23.250.1 netmask 255.255.255.0
# vi /etc/inetd.conf

...
tftp    dgram   udp     wait    root    /usr/libexec/tftpd      tftpd -l -s /data/tftpboot
...

Get those files from CentOS syslinux rpm and copy them to tftp directory.

# cp chain.c32 mboot.c32 memdisk menu.c32 pxelinux.0 /data/tftpboot/
# mkdir /data/tftpboot/pxelinux.cfg
# vi /data/tftpboot/pxelinux.cfg/default

default menu.c32
prompt 0
timeout 300
MENU TITLE PXE Menu
LABEL CentOS 6.5 x86_64
MENU LABEL CentOS 6.5 x86_64
KERNEL images/centos/x86_64/6.5/vmlinuz append vga=normal initrd=images/centos/x86_64/6.5/initrd.img ramdisk_size=32768
method=http://172.23.250.1/centos/6.5/os/x86_64/

# mdconfig -a -t vnode -f CentOS-6.5-x86_64-bin-DVD1.iso && mount -r -t cd9660 /dev/md0 /mnt
# mkdir -p /data/tftpboot/images/centos/x86_64/6.5/
# cp /mnt/images/pxeboot/* /data/tftpboot/images/centos/x86_64/6.5/
# mkdir -p /data/www/centos/6.5/os/x86_64/

Copy installation files from ISO file to web directory for URL installation.

# cp -r /mnt/* /data/www/centos/6.5/os/x86_64/
# umount /mnt && mdconfig -d -u 0
# cat /usr/local/etc/dhcpd.conf

ddns-update-style none;
not authoritative;
option domain-name "local.net";
option domain-name-servers 8.8.8.8;
option subnet-mask 255.255.255.0;
subnet 172.23.250.0 netmask 255.255.255.0 {
   authoritative;
   range 172.23.250.240 172.23.250.245;
   option routers 172.23.250.1;
   allow unknown-clients;
   allow booting;
   allow bootp;
   next-server 172.23.250.1;
   filename "/pxelinux.0";
}

# /etc/rc.d/inetd onestart
# /usr/local/etc/rc.d/isc-dhcpd onestart