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     lagg — link aggregation and link failover interface


     To compile this driver into the kernel, place the following line in your kernel
     configuration file:

           device lagg

     Alternatively, to load the driver as a module at boot time, place the following line in



     The lagg interface allows aggregation of multiple network interfaces as one virtual lagg
     interface for the purpose of providing fault-tolerance and high-speed links.

     A lagg interface can be created using the ifconfig laggN create command.  It can use
     different link aggregation protocols specified using the laggproto proto option.  Child
     interfaces can be added using the laggport child-iface option and removed using the
     -laggport child-iface option.

     The driver currently supports the aggregation protocols failover (the default), lacp,
     loadbalance, roundrobin, broadcast, and none.  The protocols determine which ports are used
     for outgoing traffic and whether a specific port accepts incoming traffic.  The interface
     link state is used to validate if the port is active or not.

     failover     Sends traffic only through the active port.  If the master port becomes
                  unavailable, the next active port is used.  The first interface added is the
                  master port; any interfaces added after that are used as failover devices.

                  By default, received traffic is only accepted when they are received through
                  the active port.  This constraint can be relaxed by setting the
         sysctl(8) variable to a nonzero value, which is
                  useful for certain bridged network setups.

     lacp         Supports the IEEE 802.1AX (formerly 802.3ad) Link Aggregation Control Protocol
                  (LACP) and the Marker Protocol.  LACP will negotiate a set of aggregable links
                  with the peer in to one or more Link Aggregated Groups.  Each LAG is composed
                  of ports of the same speed, set to full-duplex operation.  The traffic will be
                  balanced across the ports in the LAG with the greatest total speed, in most
                  cases there will only be one LAG which contains all ports.  In the event of
                  changes in physical connectivity, Link Aggregation will quickly converge to a
                  new configuration.

     loadbalance  Balances outgoing traffic across the active ports based on hashed protocol
                  header information and accepts incoming traffic from any active port.  This is
                  a static setup and does not negotiate aggregation with the peer or exchange
                  frames to monitor the link.  The hash includes the Ethernet source and
                  destination address, and, if available, the VLAN tag, and the IP source and
                  destination address.

     roundrobin   Distributes outgoing traffic using a round-robin scheduler through all active
                  ports and accepts incoming traffic from any active port.  Using roundrobin mode
                  can cause unordered packet arrival at the client.  Throughput might be limited
                  as the client performs CPU-intensive packet reordering.

     broadcast    Sends frames to all ports of the LAG and receives frames on any port of the

     none         This protocol is intended to do nothing: it disables any traffic without
                  disabling the lagg interface itself.

     Each lagg interface is created at runtime using interface cloning.  This is most easily done
     with the ifconfig(8) create command or using the cloned_interfaces variable in rc.conf(5).

     The MTU of the first interface to be added is used as the lagg MTU.  All additional
     interfaces are required to have exactly the same value.

     The loadbalance and lacp modes will use the RSS hash from the network card if available to
     avoid computing one, this may give poor traffic distribution if the hash is invalid or uses
     less of the protocol header information.  Local hash computation can be forced per interface
     by setting the -use_flowid ifconfig(8) flag.  The default for new interfaces is set via the sysctl(8).


     Create a link aggregation using LACP with two bge(4) Gigabit Ethernet interfaces:

           # ifconfig bge0 up
           # ifconfig bge1 up
           # ifconfig lagg0 create
           # ifconfig lagg0 laggproto lacp laggport bge0 laggport bge1 \

     Create a link aggregation using ROUNDROBIN with two bge(4) Gigabit Ethernet interfaces and
     set a stride of 500 packets per interface:

           # ifconfig bge0 up
           # ifconfig bge1 up
           # ifconfig lagg0 create
           # ifconfig lagg0 laggproto roundrobin laggport bge0 laggport bge1 \
           # ifconfig lagg0 rr_limit 500

     The following example uses an active failover interface to set up roaming between wired and
     wireless networks using two network devices.  Whenever the wired master interface is
     unplugged, the wireless failover device will be used:

           # ifconfig em0 up
           # ifconfig ath0 ether 00:11:22:33:44:55
           # ifconfig create wlan0 wlandev ath0 ssid my_net up
           # ifconfig lagg0 create
           # ifconfig lagg0 laggproto failover laggport em0 laggport wlan0 \

     (Note the mac address of the wireless device is forced to match the wired device as a


     ng_one2many(4), ifconfig(8), sysctl(8)


     The lagg device first appeared in FreeBSD 6.3.


     The lagg driver was written under the name trunk by Reyk Floeter <>.  The
     LACP implementation was written by YAMAMOTO Takashi for NetBSD.


     There is no way to configure LACP administrative variables, including system and port
     priorities.  The current implementation always performs active-mode LACP and uses 0x8000 as
     system and port priorities.