Jails in FreeBSD provide a simple yet flexible way to set up a proper server layout. In the most setups the actual server only acts as the host system for the jails while the applications themselves run within those independent containers. Traditionally every jail has it’s own IP for the user to be able to address the individual services. But if you’re still using IPv4 this might get you in trouble as the most hosters don’t offer more than one single public IP address per server.
Create the internal network
In this case NAT (“Network Address Translation”) is a good way to expose services in different jails using the same IP address.
First, let’s create an internal network (“NAT network”) at
You could generally use any private IPv4 address space as specified in
RFC 1918. Here’s an overview:
pf, FreeBSD’s firewall,
we will map requests on different ports of the same public IP address to our
individual jails as well as provide network access to the jails themselves.
First let’s check which network devices are available. In my case there’s
which provides connectivity to the internet and
lo0, the local loopback device.
em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500 options=209b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,WOL_MAGIC> [...] inet 172.31.1.100 netmask 0xffffff00 broadcast 172.31.1.255 nd6 options=23<PERFORMNUD,ACCEPT_RTADV,AUTO_LINKLOCAL> media: Ethernet autoselect (1000baseT <full-duplex>) status: active lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384 options=600003<RXCSUM,TXCSUM,RXCSUM_IPV6,TXCSUM_IPV6> inet6 ::1 prefixlen 128 inet6 fe80::1%lo0 prefixlen 64 scopeid 0x2 inet 127.0.0.1 netmask 0xff000000 nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
For our internal network, we create a cloned loopback device called
Therefore we need to customize the
/etc/rc.conf file, adding the following two lines:
This defines a
/29 network, offering IP addresses for a maximum of 6 jails:
ipcalc 192.168.0.1/29 Address: 192.168.0.1 11000000.10101000.00000000.00000 001 Netmask: 255.255.255.248 = 29 11111111.11111111.11111111.11111 000 Wildcard: 0.0.0.7 00000000.00000000.00000000.00000 111 => Network: 192.168.0.0/29 11000000.10101000.00000000.00000 000 HostMin: 192.168.0.1 11000000.10101000.00000000.00000 001 HostMax: 192.168.0.6 11000000.10101000.00000000.00000 110 Broadcast: 192.168.0.7 11000000.10101000.00000000.00000 111 Hosts/Net: 6 Class C, Private Internet
Then we need to restart the network. Please be aware of currently active SSH sessions as they might be dropped during restart. It’s a good moment to ensure you have KVM access to that server ;-)
service netif restart
After reconnecting, our newly created loopback device is active:
lo1: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384 options=600003<RXCSUM,TXCSUM,RXCSUM_IPV6,TXCSUM_IPV6> inet 192.168.0.1 netmask 0xfffffff8 inet 192.168.0.2 netmask 0xffffffff inet 192.168.0.3 netmask 0xffffffff inet 192.168.0.4 netmask 0xffffffff inet 192.168.0.5 netmask 0xffffffff inet 192.168.0.6 netmask 0xffffffff inet 192.168.0.7 netmask 0xffffffff inet 192.168.0.8 netmask 0xffffffff inet 192.168.0.9 netmask 0xffffffff nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
pf part of the FreeBSD base system, so we only have to configure and enable it.
By this moment you should already have a clue of which services you want to expose.
If this is not the case, just fix that file later on. In my example
configuration, I have a jail running a webserver and another jail running a
# Public IP address IP_PUB="184.108.40.206" # Packet normalization scrub in all # Allow outbound connections from within the jails nat on em0 from lo1:network to any -> (em0) # webserver jail at 192.168.0.2 rdr on em0 proto tcp from any to $IP_PUB port 443 -> 192.168.0.2 # just an example in case you want to redirect to another port within your jail rdr on em0 proto tcp from any to $IP_PUB port 80 -> 192.168.0.2 port 8080 # mailserver jail at 192.168.0.3 rdr on em0 proto tcp from any to $IP_PUB port 25 -> 192.168.0.3 rdr on em0 proto tcp from any to $IP_PUB port 587 -> 192.168.0.3 rdr on em0 proto tcp from any to $IP_PUB port 143 -> 192.168.0.3 rdr on em0 proto tcp from any to $IP_PUB port 993 -> 192.168.0.3
Now just enable
pf like this (which is the equivalent of adding
and start it:
service pf start
Ezjail is a collection of scripts by erdgeist that allow you to easily manage your jails.
pkg install ezjail
As an alternative, you could install
ezjail from the ports tree. Now we need
to set up the
basejail which contains the shared base system for our jails. In fact, every jail that
you create get’s will use that
basejail to symlink directories related to the base system like
This can be accomplished by running
In the next step, we’ll copy the
/etc/resolv.conf file from our host to the
newjail, which is the template for newly created jails (the parts that are not provided by
basejail), to ensure that domain
resolution will work properly within our jails later on:
cp /etc/resolv.conf /usr/jails/newjail/etc/
Last but not least, we enable
ezjail and start it:
sysrc ezjail_enable="YES" service ezjail start
Create a jail
Creating a jail is as easy as it could probably be:
ezjail-admin create webserver 192.168.0.2 ezjail-admin start webserver
Now you can access your jail using:
ezjail-admin console webserver
Each jail contains a vanilla FreeBSD installation.
Now you can spin up as many jails as you want to set up your services like web,
mail or file shares. You should take care not to enable
sshd within your jails,
because that would cause problems with the service’s IP bindings. But this is not
a problem, just SSH to the host and enter your jail using
I run this site without advertisement of any kind. All information is free and my only goal is to give back something to the amazing free software development community. If you find some value in this, please consider donating me a cup of coffee using PayPal. Thank you so much!