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.

An example of setting up an LACP bonded pair in Debian Wheezy can be found in the article Xen Networking

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.

     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 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.

     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 policy: transmits everything on all slave
     interfaces.  This mode provides fault tolerance.

     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.

     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.

     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.
     

• http://serverfault.com/questions/446911/what-are-the-differences-between-channel-bonding-modes-in-linux