Please provide a short (approximately 100 word) summary of the following web Content, written in the voice of the original author. If there is anything controversial please highlight the controversy. If there is something surprising, unique, or clever, please highlight that as well. Content:
Title: Jails on FreeBSD
Site: ogris.de

 Jails on FreeBSD 
 We have had  Jails  on FreeBSD since 4.0 came out 19 years ago in March 2000. This describes how to setup jails on FreeBSD 12 without any helpers. 
 Steps 
 
 I usually place all jails under  /var/jail  and give each jail its own directory, which reflects its short hostname. For this, I use  bsdinstall :
 # bsdinstall jail /var/jail/mysql 
Deselect all optional system components during the installation as well as any services.
 
 On the host system, you can either create one big  /etc/jail.conf  or one  /etc/jail.HOSTNAME.conf  per jail, e.g.  /etc/jail.mysql.conf :
 
exec.start = "/bin/sh /etc/rc";
exec.stop = "/bin/sh /etc/rc.shutdown";
exec.clean;
mount.devfs;

path = "/var/jail/mysql";

mysql {
  host.hostname = "mysql.intra.ogris.net";
  ip4.addr = "lo1|10.0.0.2";
}
 
 In order to have the jails started and stopped during system boot and shutdown, respectively, add this to  /etc/rc.conf :
 
jail_enable="YES"
jail_list="mysql"
 
 Unless you want to assign each jail an IP address from your network, you have to setup a host-only network. In  /etc/rc.conf :
 
cloned_interfaces="lo1"
ifconfig_lo1="inet 10.0.0.1 netmask 255.255.255.0"
 
 Usually, you want to give your jails Internet access. Thus, we need NAT on the host. First, create  /etc/ipfw.rules :
 
nat 1 config if vtnet0 same_ports
add nat 1 ip from any to any via vtnet0
add allow ip from any to any
 
Replace  vtnet0  by your actual network interface. 
 Now add this to  /etc/rc.conf  in order to activate IP forwarding and to have the firewall rules loaded during system boot:
 
kld_list="ipfw_nat"
gateway_enable="YES"
firewall_enable="YES"
firewall_type="/etc/ipfw.rules"
 
 Reboot the host. Afterwards, you can log into your jails, e.g. by typing
 
# jexec mysql /bin/csh
 
 Optionally, set up a local  unbound  as caching DNS resolver:
 
# cat >/etc/unbound/conf.d/local.conf <<EOF
server:
	interface: 0.0.0.0
	access-control: 127.0.0.0/8 allow
	access-control: 10.0.0.0/24 allow
EOF
# service local_unbound enable
# service local_unbound start
 
 Inside the jail, setup  /etc/resolv.conf  (you can do this from the host as well!). Either add your local nameserver, or the jail's IP address if you started a local unbound resolver on the host as described above 
 Now, you can install the ports collections as usual:
 
# portsnap fetch extract
 
 Not strictly needed, but I like my jails to send emails via the host system. First, fix  /etc/make.conf  for both the host and the jails:
 
SENDMAIL_MC=/etc/mail/freebsd.mc
SENDMAIL_SUBMIT_MC=/etc/mail/freebsd.submit.mc
 
 On the host, add this to  /etc/rc.conf :
 
sendmail_enable="YES"
sendmail_rebuild_aliases="YES"
 
 Make sure that  /etc/mail/freebsd.mc  contains these lines:
 
FEATURE(`accept_unresolvable_domains')dnl
FEATURE(`accept_unqualified_senders')dnl
DAEMON_OPTIONS(`Name=IPv4, Family=inet, Addr=10.0.0.1')dnl
 
 Additionally, if your host has to use a relay server as well:
 
define(`SMART_HOST', `[192.168.23.42]')dnl
 
 Rebuild sendmail.cf and restart sendmail:
 
# make -C /etc/mail clean all install
# service sendmail restart
 
 Inside each jail, add this to  /etc/rc.conf :
 
sendmail_rebuild_aliases="YES"
 
 In  /etc/mail/freebsd.mc , set the host's ip address as relay server:
 
define(`SMART_HOST', `[10.0.0.1]')dnl
FEATURE(nocanonify)dnl
 
 Rebuild sendmail.cf and restart sendmail inside the jails as well:
 
# make -C /etc/mail clean all install
# service sendmail restart
 
 
 Updating jails 
 I wrote and have used  jupdate.sh  to run  freebsd-update ,  postsnap , and  portmaster  on the host system and inside each running jail.