https://cdn-learn.adafruit.com/downloads/pdf/setting-up-a-raspberry-pi-as-a-wifi-access-point.pdf

apt-get install hostapd isc-dhcp-server iptables-persistent

edit /etc/dhcp/dhcpd.conf

Comentar 
  #option domain-name "example.org";
  #option domain-name-servers ns1.example.org, ns2.example.org;

Find the lines that say
  # If this DHCP server is the official DHCP server for the local
  # network, the authoritative directive should be uncommented.
  #authoritative;

and remove the # so it says
  # If this DHCP server is the official DHCP server for the local
  # network, the authoritative directive should be uncommented.
  authoritative;


<code>
subnet 192.168.42.0 netmask 255.255.255.0 {
 range 192.168.42.10 192.168.42.50;
 option broadcast-address 192.168.42.255;
 option routers 192.168.42.1;
 default-lease-time 600;
 max-lease-time 7200;
 option domain-name "local";
 option domain-name-servers 8.8.8.8, 8.8.4.4;
}
</code>

  sudo nano /etc/default/isc-dhcp-server

  INTERFACES="" 
and update it to say 
  INTERFACES="wlan0"

Comentamos wlan0 en /etc/network/interfaces

iface wlan0 inet static
  address 192.168.42.1
  netmask 255.255.255.0
  
Creamos el fichero nuevo:
  /etc/hostapd/hostapd.conf
Con el adaptor wifi interno raspi3 comentamos la línea de driver:

<code>
interface=wlan0
#driver=rtl871xdrv
ssid=Pi_AP
country_code=US
hw_mode=g
channel=6
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=2
wpa_passphrase=Raspberry
wpa_key_mgmt=WPA-PSK
wpa_pairwise=CCMP
wpa_group_rekey=86400
ieee80211n=1
wme_enabled=1
</code>


Añadimos al fichero
  /etc/default/hostapd
La línea:
  DAEMON_CONF="/etc/hostapd/hostapd.conf"


  /etc/init.d/hostapd
  DAEMON_CONF=/etc/hostapd/hostapd.conf