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FreeBSD provides the <citerefentry><refentrytitle>lagg</refentrytitle><manvolnum>4</manvolnum></citerefentry> interface which can be used to aggregate multiple network interfaces into one virtual interface in order to provide failover and link aggregation. Failover allows traffic to continue to flow as long as at least one aggregated network interface has an established link. Link aggregation works best on switches which support <acronym>LACP</acronym>, as this protocol distributes traffic bi-directionally while responding to the failure of individual links.
The aggregation protocols supported by the lagg interface determine which ports are used for outgoing traffic and whether or not a specific port accepts incoming traffic. The following protocols are supported by <citerefentry><refentrytitle>lagg</refentrytitle><manvolnum>4</manvolnum></citerefentry>:
This mode sends and receives traffic only through the master port. If the master port becomes unavailable, the next active port is used. The first interface added to the virtual interface is the master port and all subsequently added interfaces are used as failover devices. If failover to a non-master port occurs, the original port becomes master once it becomes available again.
fec / loadbalance
<trademark class="registered">Cisco</trademark> Fast <trademark class="registered">EtherChannel</trademark> (<acronym>FEC</acronym>) is found on older <trademark class="registered">Cisco</trademark> switches. It provides a static setup and does not negotiate aggregation with the peer or exchange frames to monitor the link. If the switch supports <acronym>LACP</acronym>, that should be used instead.
The <trademark class="registered">IEEE</trademark> 802.3ad Link Aggregation Control Protocol (<acronym>LACP</acronym>) negotiates a set of aggregable links with the peer into one or more Link Aggregated Groups (<acronym>LAG</acronym>s). Each <acronym>LAG</acronym> is composed of ports of the same speed, set to full-duplex operation, and traffic is balanced across the ports in the <acronym>LAG</acronym> with the greatest total speed. Typically, there is only one <acronym>LAG</acronym> which contains all the ports. In the event of changes in physical connectivity, <acronym>LACP</acronym> will quickly converge to a new configuration.
<acronym>LACP</acronym> balances outgoing traffic across the active ports based on hashed protocol header information and accepts incoming traffic from any active port. The hash includes the Ethernet source and destination address and, if available, the <acronym>VLAN</acronym> tag, and the <acronym>IPv4</acronym> or <acronym>IPv6</acronym> source and destination address.
This mode distributes outgoing traffic using a round-robin scheduler through all active ports and accepts incoming traffic from any active port. Since this mode violates Ethernet frame ordering, it should be used with caution.
Configuration Examples
This section demonstrates how to configure a <trademark class="registered">Cisco</trademark> switch and a FreeBSD system for <acronym>LACP</acronym> load balancing. It then shows how to configure two Ethernet interfaces in failover mode as well as how to configure failover mode between an Ethernet and a wireless interface.
<acronym>LACP</acronym> Aggregation with a <trademark class="registered">Cisco</trademark> Switch
This example connects two <citerefentry><refentrytitle>fxp</refentrytitle><manvolnum>4</manvolnum></citerefentry> Ethernet interfaces on a FreeBSD machine to the first two Ethernet ports on a <trademark class="registered">Cisco</trademark> 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 <trademark class="registered">Cisco</trademark> ports, Ethernet devices, channel group number, and <acronym>IP</acronym> 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 <trademark class="registered">Cisco</trademark> switch, add the <replaceable>FastEthernet0/1</replaceable> and <replaceable>FastEthernet0/2</replaceable> interfaces to channel group <replaceable>1</replaceable>:
<userinput>interface <replaceable>FastEthernet0/1</replaceable>
channel-group <replaceable>1</replaceable> mode active
channel-protocol lacp</userinput>
<userinput>interface <replaceable>FastEthernet0/2</replaceable>
channel-group <replaceable>1</replaceable> mode active
channel-protocol lacp</userinput>
On the FreeBSD system, create the <citerefentry><refentrytitle>lagg</refentrytitle><manvolnum>4</manvolnum></citerefentry> interface using the physical interfaces <replaceable>fxp0</replaceable> and <replaceable>fxp1</replaceable> and bring the interfaces up with an <acronym>IP</acronym> address of <replaceable></replaceable>:
<prompt>#</prompt> <userinput>ifconfig <replaceable>fxp0</replaceable> up</userinput>
<prompt>#</prompt> <userinput>ifconfig <replaceable>fxp1</replaceable> up</userinput>
<prompt>#</prompt> <userinput>ifconfig <literal>lagg<replaceable>0</replaceable></literal> create </userinput>
<prompt>#</prompt> <userinput>ifconfig <literal>lagg<replaceable>0</replaceable></literal> up laggproto lacp laggport <replaceable>fxp0</replaceable> laggport <replaceable>fxp1</replaceable> <replaceable></replaceable></userinput>
Next, verify the status of the virtual interface:
<prompt>#</prompt> <userinput>ifconfig <literal>lagg<replaceable>0</replaceable></literal></userinput>
lagg0: flags=8843&lt;UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST&gt; metric 0 mtu 1500
ether 00:05:5d:71:8d:b8
inet netmask 0xffffff00 broadcast
media: Ethernet autoselect
status: active
laggproto lacp
laggport: fxp1 flags=1c&lt;ACTIVE,COLLECTING,DISTRIBUTING&gt;
laggport: fxp0 flags=1c&lt;ACTIVE,COLLECTING,DISTRIBUTING&gt;
Ports marked as <literal>ACTIVE</literal> are part of the <acronym>LAG</acronym> that has been negotiated with the remote switch. Traffic will be transmitted and received through these active ports. Add <option>-v</option> to the above command to view the <acronym>LAG</acronym> identifiers.
To see the port status on the <trademark class="registered">Cisco</trademark> switch:
switch# <userinput>show lacp neighbor</userinput>
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 <userinput>show lacp neighbor detail</userinput>.


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books/handbook.pot, string 11053