LAGG(4) FreeBSD Kernel Interfaces Manual LAGG(4)


lagglink 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 loader.conf(5):



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), fec, lacp, loadbalance, roundrobin, 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.

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 net.link.lagg.failover_rx_all sysctl(8) variable to a nonzero value, which is useful for certain bridged network setups.

Supports Cisco EtherChannel. This is an alias for loadbalance mode.
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.
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.
Distributes outgoing traffic using a round-robin scheduler through all active ports and accepts incoming traffic from any active port.
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 net.link.lagg.X.use_flowid sysctl(8) variable to zero where X is the interface number. The default for new interfaces is set via the net.link.lagg.default_use_flowid sysctl(8).


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

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

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 laggproto failover laggport em0 laggport wlan0 \ netmask

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


The lagg device first appeared in FreeBSD 6.3.


The lagg driver was written under the name trunk by Reyk Floeter <reyk@openbsd.org>. 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.
February 23, 2012 FreeBSD