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lagg (Link Aggregation and link failover interface)


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.

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.
Supports the IEEE 802.3AX (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 adtress.
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.
Sends frames to all ports of the LAG and receives frames on any port of the LAG.
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 ie1g0 up
# ifconfig ie1g1 up
# ifconfig lagg0 laggproto lacp laggport ie1g0 laggport ie1g1 \ netmask

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

# ifconfig ie1g0 up
# ifconfig ie1g1 up
# ifconfig lagg0 create
# ifconfig lagg0 laggproto roundrobin laggport ie1g0 laggport    ie1g1 \ netmask
# ifconfig lagg0 rr_limit 500


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.

See Also