This example connects two fxp(4) Ethernet interfaces on a FreeBSD machine to the first two Ethernet ports on a Cisco® switch as a single load balanced and fault tolerant link. More interfaces can be added to increase throughput and fault tolerance. Replace the names of the Cisco® ports, Ethernet devices, channel group number, and IP address shown in the example to match the local configuration.

Frame ordering is mandatory on Ethernet links and any traffic between two stations always flows over the same physical link, limiting the maximum speed to that of one interface. The transmit algorithm attempts to use as much information as it can to distinguish different traffic flows and balance the flows across the available interfaces.

On the Cisco® switch, add the FastEthernet0/1 and FastEthernet0/2 interfaces to channel group 1:

interface FastEthernet0/1
 channel-group 1 mode active
 channel-protocol lacp
!
interface FastEthernet0/2
 channel-group 1 mode active
 channel-protocol lacp

On the FreeBSD system, create the lagg(4) interface using the physical interfaces fxp0 and fxp1 and bring the interfaces up with an IP address of 10.0.0.3/24:

# ifconfig fxp0 up
# ifconfig fxp1 up
# ifconfig lagg0 create 
# ifconfig lagg0 up laggproto lacp laggport fxp0 laggport fxp1 10.0.0.3/24

Next, verify the status of the virtual interface:

# ifconfig lagg0
lagg0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
        options=8<VLAN_MTU>
        ether 00:05:5d:71:8d:b8
        inet 10.0.0.3 netmask 0xffffff00 broadcast 10.0.0.255
        media: Ethernet autoselect
        status: active
        laggproto lacp
        laggport: fxp1 flags=1c<ACTIVE,COLLECTING,DISTRIBUTING>
        laggport: fxp0 flags=1c<ACTIVE,COLLECTING,DISTRIBUTING>

Ports marked as ACTIVE are part of the LAG that has been negotiated with the remote switch. Traffic will be transmitted and received through these active ports. Add -v to the above command to view the LAG identifiers.

To see the port status on the Cisco® switch:

switch# show lacp neighbor
Flags:  S - Device is requesting Slow LACPDUs
        F - Device is requesting Fast LACPDUs
        A - Device is in Active mode       P - Device is in Passive mode

Channel group 1 neighbors

Partner's information:

                  LACP port                        Oper    Port     Port
Port      Flags   Priority  Dev ID         Age     Key     Number   State
Fa0/1     SA      32768     0005.5d71.8db8  29s    0x146   0x3      0x3D
Fa0/2     SA      32768     0005.5d71.8db8  29s    0x146   0x4      0x3D

For more detail, type show lacp neighbor detail.

To retain this configuration across reboots, add the following entries to /etc/rc.conf on the FreeBSD system:

ifconfig_fxp0="up"
ifconfig_fxp1="up"
cloned_interfaces="lagg0"
ifconfig_lagg0="laggproto lacp laggport fxp0 laggport fxp1 10.0.0.3/24"

Failover mode can be used to switch over to a secondary interface if the link is lost on the master interface. To configure failover, make sure that the underlying physical interfaces are up, then create the lagg(4) interface. In this example, fxp0 is the master interface, fxp1 is the secondary interface, and the virtual interface is assigned an IP address of 10.0.0.15/24:

# ifconfig fxp0 up
# ifconfig fxp1 up
# ifconfig lagg0 create
# ifconfig lagg0 up laggproto failover laggport fxp0 laggport fxp1 10.0.0.15/24

The virtual interface should look something like this:

# ifconfig lagg0
lagg0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
        options=8<VLAN_MTU>
        ether 00:05:5d:71:8d:b8
        inet 10.0.0.15 netmask 0xffffff00 broadcast 10.0.0.255
        media: Ethernet autoselect
        status: active
        laggproto failover
        laggport: fxp1 flags=0<>
        laggport: fxp0 flags=5<MASTER,ACTIVE>

Traffic will be transmitted and received on fxp0. If the link is lost on fxp0, fxp1 will become the active link. If the link is restored on the master interface, it will once again become the active link.

To retain this configuration across reboots, add the following entries to /etc/rc.conf:

ifconfig_fxp0="up"
ifconfig_fxp1="up"
cloned_interfaces="lagg0"
ifconfig_lagg0="laggproto failover laggport fxp0 laggport fxp1 10.0.0.15/24"

For laptop users, it is usually desirable to configure the wireless device as a secondary which is only used when the Ethernet connection is not available. With lagg(4), it is possible to configure a failover which prefers the Ethernet connection for both performance and security reasons, while maintaining the ability to transfer data over the wireless connection.

This is achieved by overriding the physical wireless interface's MAC address with that of the Ethernet interface.

In this example, the Ethernet interface, bge0, is the master and the wireless interface, wlan0, is the failover. The wlan0 device was created from iwn0 wireless interface, which will be configured with the MAC address of the Ethernet interface. First, determine the MAC address of the Ethernet interface:

# ifconfig bge0
bge0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
	options=19b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,TSO4>
	ether 00:21:70:da:ae:37
	inet6 fe80::221:70ff:feda:ae37%bge0 prefixlen 64 scopeid 0x2
	nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
	media: Ethernet autoselect (1000baseT <full-duplex>)
	status: active

Replace bge0 to match the system's Ethernet interface name. The ether line will contain the MAC address of the specified interface. Now, change the MAC address of the underlying wireless interface:

# ifconfig iwn0 ether 00:21:70:da:ae:37

Bring the wireless interface up, but do not set an IP address:

# ifconfig wlan0 create wlandev iwn0 ssid my_router up

Make sure the bge0 interface is up, then create the lagg(4) interface with bge0 as master with failover to wlan0:

# ifconfig bge0 up
# ifconfig lagg0 create
# ifconfig lagg0 up laggproto failover laggport bge0 laggport wlan0

The virtual interface should look something like this:

# ifconfig lagg0
lagg0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
        options=8<VLAN_MTU>
        ether 00:21:70:da:ae:37
        media: Ethernet autoselect
        status: active
        laggproto failover
        laggport: wlan0 flags=0<>
        laggport: bge0 flags=5<MASTER,ACTIVE>

Then, start the DHCP client to obtain an IP address:

# dhclient lagg0

To retain this configuration across reboots, add the following entries to /etc/rc.conf:

ifconfig_bge0="up"
wlans_iwn0="wlan0"
ifconfig_wlan0="WPA"
create_args_wlan0="wlanaddr 00:21:70:da:ae:37"
cloned_interfaces="lagg0"
ifconfig_lagg0="up laggproto failover laggport bge0 laggport wlan0 DHCP"