Jails have multiple networking options to better serve a user’s needs. Traditionally, jails have only supported IP alias based networking. This is where an IP address is assigned to the host’s interface and then used by the jail for network communication. This is typically known as “shared IP” based jails.

Another recently developed option is called VNET or sometimes VIMAGE. VNET is a fully virtualized networking stack which is isolated per jail. VNET abstracts virtual network interfaces to jails, which then behave in the same way as physical interfaces.

By default, iocage does not enable VNET, but users can enable and configure VNET for a jail by configuring that jail’s properties using the instructions in the Configure a Jail section of this documentation.

The rest of this section shows more depth of the Shared IP and VNET networking options, along with instructions for Configuring Network Interfaces.


In the examples in this section, em0 is used as the network adapter. em0 is a placeholder and must be replaced with the user’s specific network adapter. A network adapter is a computer hardware component that connects a computer to a computer network. In order to find the network adapter on the system run ifconfig.

Shared IP

The Shared IP networking option is rock solid, with over a decade of heavy use and testing.

It has no specific system requirements, as everything needed is built directly into the default GENERIC kernel.

Using Shared IP

There are a few steps to follow when setting up Shared IP:

Check the VNET property status

# iocage get vnet examplejail1

If vnet is on, disable it:

# iocage set vnet=off examplejail1

Configure an IP address

# iocage set ip4_addr="em0|" examplejail1

If multiple addresses are desired, separate the configuration directives with a ,:

# iocage set ip4_addr="em0|,em0|" examplejail1

Start the jail

iocage start examplejail1

Verify visible IP configuration in the jail

# iocage exec examplejail1 ifconfig


VNET is considered experimental. Unexpected system crashes can occur. More details about issues with VNET are available in the Known Issues section of this documentation.

There are a number of required steps when configuring a jail to use VNET:



If not required, disable SCTP.

Rebuild the kernel with these options:

nooptions       SCTP   # Stream Control Transmission Protocol
options         VIMAGE # VNET/Vimage support
options         RACCT  # Resource containers
options         RCTL   # same as above


On the host node, add this bridge configuration to /etc/rc.conf:

# set up bridge interface for iocage

# plumb interface em0 into bridge0
ifconfig_bridge0="addm em0 up"


Add these tunables to /etc/sysctl.conf:

net.inet.ip.forwarding=1       # Enable IP forwarding between interfaces  # Only pass IP packets when pfil is enabled  # Packet filter on the bridge interface  # Packet filter on the member interface

Enable vnet for the jail

# iocage set vnet=on examplejail

Configure jail’s default gateway

# iocage set defaultrouter= examplejail

Configure an IP address

iocage set ip4_addr="vnet0|" examplejail

Start jail and ping the default gateway

Start the jail:

# iocage start examplejail

Open the system console inside the jail:

iocage console examplejail

Ping the previously configured default gateway:

# ping



Be sure the default gateway knows the route back to the VNET subnets.

Using VLANs

To assign a jail’s traffic to a VLAN, add the VLAN interface as a bridge member, but not the VLAN’s parent. For example:

sysrc vlans_em0="666"
sysrc ifconfig_em0_666="up"
iocage set vnet_default_interface="em0.666" examplejail
iocage set interfaces="vnet1:bridge1" examplejail

If using VLAN interfaces for the jail host only, on the other hand, add the parent as a bridge member, but not the VLAN interface.

sysrc vlans_em0="666"
sysrc ifconfig_em0_666=""
iocage set vnet_default_interface="auto" examplejail # "em0" would also work
iocage set interfaces="vnet1:bridge1" examplejail

Configuring Network Interfaces

iocage transparently handles network configuration for both Shared IP and VNET jails.

Configuring a Shared IP Jail


# iocage set ip4_addr="em0|" examplejail


# iocage set ip6_addr="em0|2001:123:456:242::5/64" examplejail

These examples add IP alias and 2001:123:456::5/64 to interface em0 of the shared IP jail, at start time.

Configuring a VNET Jail

To configure both IPv4 and IPv6:

# iocage set ip4_addr="vnet0|" examplejail

# iocage set ip6_addr="vnet0|2001:123:456:242::5/64" examplejail

# iocage set defaultrouter6="2001:123:456:242::1" examplejail


For VNET jails, a default route has to also be specified.

To create a a jail with a DHCP interface add the dhcp=on property:

# iocage create -r 11.0-RELEASE --name myjail dhcp=on

The dhcp=on property implies creating a VNET virtual network stack and enabling the Berkley Packet Filter. DHCP cannot work without VNET. More information about VNET is available in the VNET(9) FreeBSD manual page.

Tips for Configuring VNET

To start a jail with no IPv4/6 address, set the ip4_addr and ip6_addr properties, then the defaultrouter and defaultrouter6 properties:

# iocage set ip4_addr=none ip6_addr=none examplejail

# iocage set defaultrouter=none defaultrouter6=none examplejail

Force iocage to regenerate the MAC and HW address (e.g.: after cloning a jail). This will cause the MAC and HW addresses to be regenerated when the jail is next started.

# iocage set vnet0_mac=none examplejail