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====== LACP (aka bonding) ======

Link Aggregation, also known as //bonding// in Linux, uses two or more network interfaces to make one //aggregate// interface. This is designed for speed and redundancy.

With Link Aggregation, traffic may be spread across the multiple lines, increasing speed, or increasing fault tolerance by moving data seamlessly from one line to another in case of network failure. Combinations of these are available.

===== Implementation =====

An example of setting up an LACP bonded pair in Debian Wheezy can be found in the article [[unix:virtualization:xen:networking]]

===== LACP modes =====
LACP has several different modes which are combinations of the above. Some of the modes require network switches that "talk" LACP, though modes 0, 1, 5 & 6 do not.

==== balance-rr (mode 0) ====
       Round-robin policy: Transmit packets in sequential
       order from the first available slave through the
       last. This mode provides load balancing and fault
       tolerance. 


==== active-backup (mode 1) ====
       Active-backup policy: Only one slave in the bond is
       active.  A different slave becomes active if, and only
       if, the active slave fails. The bond's MAC address is
       externally visible on only one port (network adapter)
       to avoid confusing the switch.

       This mode provides fault tolerance. The "primary"
       option affects the behavior of this mode.

==== balance-xor (mode 2) ====
       XOR policy: Transmit based on the selected transmit
       hash policy.  The default policy is a simple [(source
       MAC address XOR'd with destination MAC address) modulo
       slave count].  Alternate transmit policies may be
       selected via the xmit_hash_policy option.

       This mode provides load balancing and fault tolerance.

==== broadcast (mode 3) ====
       Broadcast policy: transmits everything on all slave
       interfaces.  This mode provides fault tolerance.

==== 802.3ad (mode 4) ====
       IEEE 802.3ad Dynamic link aggregation.  Creates
       aggregation groups that share the same speed and
       duplex settings.  Utilizes all slaves in the active
       aggregator according to the 802.3ad specification.

       Slave selection for outgoing traffic is done according
       to the transmit hash policy, which may be changed from
       the default simple XOR policy via the xmit_hash_policy
       option. Note that not all transmit policies may be 802.3ad
       compliant, particularly inregards to the packet mis-ordering
       requirements of section 43.2.4 of the 802.3ad standard.
       Differing peer implementations will have varying tolerances for
       noncompliance.

       Note: Most switches will require some type of configuration
       to enable 802.3ad mode.

==== balance-tlb (mode 5) ====
       Adaptive transmit load balancing: channel bonding that
       does not require any special switch support.  The
       outgoing traffic is distributed according to the
       current load (computed relative to the speed) on each
       slave.  Incoming traffic is received by the current
       slave.  If the receiving slave fails, another slave
       takes over the MAC address of the failed receiving
       slave.

==== balance-alb (mode 6) ====
       Adaptive load balancing: includes balance-tlb plus
       receive load balancing (rlb) for IPV4 traffic, and
       does not require any special switch support.

       When a link is reconnected or a new slave joins the
       bond the receive traffic is redistributed among all
       active slaves in the bond by initiating ARP Replies
       with the selected MAC address to each of the
       clients. The updelay parameter must
       be set to a value equal or greater than the switch's
       forwarding delay so that the ARP Replies sent to the
       peers will not be blocked by the switch.
       
===== Resources =====
  * [[http://serverfault.com/questions/446911/what-are-the-differences-between-channel-bonding-modes-in-linux]]