Provided by: ubuntu-fan_0.12.13ubuntu0.1_all bug


       fanctl - fan bridge administration


       fanctl up [<options>...]
       fanctl down [<options>...]
       fanctl up -a
       fanctl down -a
       fanctl down -e
       fanctl show
       fanctl help


       fanctl  is  used  to set up, tear down, and inspect Fan bridge mappings and devices in the
       linux kernel.

       NOTE:  Future versions of the  commands  will  make  fanatic  the  primary  interface  for
              interacting  with Fan networks.  For maximum portability fanctl should only be used
              if absolutely necessary.

       A network Fan is a mechanism for expanding the  range  of  IP  addresses  available  to  a
       system.   It  is most useful for containers such as Docker and LXC/LXD, but it can be used
       in other contexts as well.  Fan works by  creating  a  bridge  that  uses  a  mathematical
       mapping  between  the  host's  (or underlay's) /16 address and the Fan's (or overlay's) /8
       address. By mapping addresses in this way, a 253-fold increase in  address  space  can  be
       achieved.   For  example, if the host machine uses a subnet of and assigns a Fan to an IP address of, the hosts's Fan overlay addresses will  be
       in  the  subnet,  where 250 is derived from the user defined overlay network


       fanctl up -u <underlay> -o <overlay> [<options>]
              Sets up a new Fan bridge mapping overlay addresses to  the  corresponding  underlay
              addresses on the local network.  Using the example, the new bridge is named fan-250
              based on the overlay and underlay addresses specified (see ADDRESSING below).   The
              options are described in the OPTIONS section below.

       fanctl down -u <underlay> -o <overlay>
              Tears  down a previously-configured Fan bridge and associated mapping.  This action
              will fail if the bridge is still in use.

       fanctl up -a
              Sets up all Fans defined in /etc/network/fan if present.

       fanctl down -a
              Tears down all automatically defined Fan bridges  on  the  system.   These  may  be
              identified in the fanctl show output via the auto flag.

       fanctl down -e
              Tears down all defined Fan bridges on the system.

       fanctl show
              Lists all currently defined Fan bridges in the system; for instance:

              # fanctl show
              Bridge       Underlay        Overlay       Flags
              fan-250   dhcp host-reserve 1

       fanctl config set -u <underlay> -o <overlay> [<options>...]
              Sets  configuration  options  for  the  underlay/overlay  combination specified (or
              clears any individual configuration if no options are specified).
              To add options, the current set of options has to be  obtained  via  fanctl  config
              show and added to the list of new options.

       fanctl config show -u <underlay> -o <overlay>
              Displays  any additional configuration options for the underlay/overlay combination

       fanctl config list
              Displays all underlay/overlay combinations which have additional configuration.

       fanctl help [<command>]
              Displays basic usage information for fanctl.  When used  with  a  specific  command
              limits output to that command.


       The  Fan  mapping is defined by a combination of the underlay and overlay addresses.  Each
       is defined as a CIDR network address.  For example:

              # fanctl up -u -o

       This example defines an overlay of and an  underlay  of   When
       mapping  an  address in the subnet, we take the 16 bits of destination address
       starting at bit 8 and replace the bottom 16 bits of the underlay  address  with  it.   For
       example, attempting to talk to will trigger the packet to be sent to
       for delivery.

       It is not always possible to know the local underlay address at the time the configuration
       is  generated  (such  as  when a common configuration is desired on all systems).  In this
       case we can specify the underlay address using only the underlay prefix, or  by  reference
       to an interface.

       For  example, to bring up a Fan bridge slice for each address in the subnet,
       the following example examines each interface as it is currently configured and configures
       a matching slice at that time:

              # fanctl up -u -o

       To  bring  up  Fan  slices  corresponding  to the addresses on a specific interface we can
       substitute the interface name:

              # fanctl up -u ens3/16 -o

       To bring up Fan slices corresponding to the addresses on  the  primary  network  interface
       (the interface with the default route), the keyword default can be substituted:

              # fanctl up -u default/16 -o


       Currently  Fan  can  only  apply  overlay  addresses  with a /8 network mask, and underlay
       addresses with a /16 network mask.  We expect to relax this limitation in a later update.


       -u <underlay>|--underlay=<underlay>
              Specify the underlay network address and mask.

       -o <overlay>|--overlay=<overlay>
              Specify the overlay network address and mask.

              Sets the encapsulation type for this Fan bridge.  May be ipip  or  vxlan  (default)
              only.  You should not normally need to specify this.

              Sets  the bridge mode.  May be compact (default) or sliced only.  In compact mode a
              single Fan bridge per overlay network is created.  In sliced mode a Fan  bridge  is
              created  for  each  local Fan slice.  sliced mode is considered legacy.  You should
              not normally need to specify this.

       --dhcp Turns on automatic address allocation for the Fan bridge.  A  dnsmasq  instance  is
              started  attached  to  the  bridge  allocating the unreserved addresses to entities
              attached to the Fan bridge.

              By default the .1 address on the Fan bridge is allocated to the host,  enabling  it
              to  communicate  with  entities  on the Fan bridge. This option reserves additional
              addresses for host applications to use. A host-reserve 4 reserves .1 through .4  in
              the Fan bridge for host use.

              By default the bridge name is based on the overlay and underlay addresses specified
              (see ADDRESSING above). This option overrides the name to one you specify.

              This option marks the Fan bridge to be automatically configured when the underlying
              interface   comes  up.   This  is  primarily  used  in  the  local  Fan  persistent
              configuration to enable centrally configured Fan mappings on a specific host.  (See
              PERSISTENT CONFIGURATION below).


       NOTE:  The  location  and  content  of  the configuration files should still be considered
       unstable as they could change in future. Use of fanatic  is  highly  recommended  as  this
       command will make any necessary changes to the right config files.

       Fan  mappings are configured via /etc/network/fan by pairs of local (underlay) and overlay
       network addresses.  The first element of each pair  specifies  the  underlay  range  which
       should be mapped into the overlay network specified by the second element. For example:

              # RFC1918 - we recommend you use these for easy interop with
              # other FAN users on small private networks. They provide
              # around 250 IP's per address, or 16 per
              # address.

              # local         overlay

       Comments are introduced via a hash (#), and blank lines are ignored.

       Note,  that  the  local  (underlay)  range  does  not need to match the subnet mask of the
       interface as long as all addresses of the larger scope are routeable. If for  example  the
       interface  is  configured  as but can reach all addresses
       that will be part of the Fan network, the local (underlay) address of  can
       be used regardless.

       It  is  expected that the /etc/network/fan configuration is globally managed ensuring that
       all hosts have consistent overlay to underlay mappings.  Local deviation  is  managed  via
       the  fanctl config subcommand.  This allow a local host to record additional flags against
       a specific overlay/underlay combination.  For example:

              # fanctl config set -u -o --enable

       will set the --enable option to the local host configuration, triggering this  Fan  to  be
       configured when the host interface is configured.


       By  default each Fan bridge represents a Fan overlay network which is expressed locally on
       the machine.  The Fan bridge will have the various slice addresses mapped to it.

       In legacy sliced mode each Fan bridge represents a slice of a Fan overlay network which is
       expressed  locally  on  the  machine.   The  Fan  bridge  will  have the overlay addresses
       representing one local IP address mapped to it.  A machine may have more  than  one  local
       address  on the underlay network, enabling it to have more than one such slice mapped.  It
       may also have more than one overlay range defined for each local IP address.

       Each Fan bridge is a separate broadcast domain, with  routing  between  the  bridges  both
       locally and globally within the Fan.

       Each  Fan bridge appears as a bridge on the system, named for the overlay subnet hosted by
       that particular Fan bridge and the underlay address prefix for which it  carries  traffic.
       For  our  on example, the bridge would be named fan-250 and would
       carry all traffic for


       fanatic(8), /usr/share/doc/ubuntu-fan/README


       Andy Whitcroft <>,
       Stefan Bader <>

                                          July 24, 2017                                 FANCTL(8)