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LACP Developer Guide

LACP Overview

The OpenDaylight LACP (Link Aggregation Control Protocol) project can be used to aggregate multiple links between OpenDaylight controlled network switches and LACP enabled legacy switches or hosts operating in active LACP mode.

OpenDaylight LACP passively negotiates automatic bundling of multiple links to form a single LAG (Link Aggregation Group). LAGs are realised in the OpenDaylight controlled switches using OpenFlow 1.3+ group table functionality.

LACP Architecture

  • inventory
    • Maintains list of OpenDaylight controlled switches and port information
    • List of LAGs created and physical ports that are part of the LAG
    • Interacts with MD-SAL to update LACP related information
  • inventorylistener
    • This module interacts with MD-SAL for receiving node/node-connector notifications
  • flow
    • Programs the switch to punt LACP PDU (Protocol Data Unit) to controller
  • packethandler
    • Receives and transmits LACP PDUs to the LACP enabled endpoint
    • Provides infrastructure services for group table programming
  • core
    • Performs LACP state machine processing

How LAG programming is implemented

The LAG representing the aggregated multiple physical ports are realized in the OpenDaylight controlled switches by creating a group table entry (Group table supported from OpenFlow 1.3 onwards). The group table entry has a group type Select and action referring to the aggregated physical ports. Any data traffic to be sent out through the LAG can be sent through the group entry available for the LAG.

Suppose there are ports P1-P8 in a node. When LACP project is installed, a group table entry for handling broadcast traffic is automatically created on all the switches that have registered to the controller.

GroupID GroupType EgressPorts
<B’castgID> ALL P1,P2,…P8

Now, assume P1 & P2 are now part of LAG1. The group table would be programmed as follows:

GroupID GroupType EgressPorts
<B’castgID> ALL P3,P4,…P8

When a second LAG, LAG2, is formed with ports P3 and P4,

GroupID GroupType EgressPorts
<B’castgID> ALL P5,P6,…P8

How applications can program OpenFlow flows using LACP-created LAG groups

OpenDaylight controller modules can get the information of LAG by listening/querying the LACP Aggregator datastore.

When any application receives packets, it can check, if the ingress port is part of a LAG by verifying the LAG Aggregator reference (lacp-agg-ref) for the source nodeConnector that OpenFlow plugin provides.

When applications want to add flows to egress out of the LAG, they must use the group entry corresponding to the LAG.

From the above example, for a flow to egress out of LAG1,

add-flow eth_type=<xxxx>,ip_dst=<x.x.x.x>,actions=output:<LAG1>

Similarly, when applications want traffic to be broadcasted, they should use the group table entries <B’castgID>,<LAG1>,<LAG2> in output action.

For all applications, the group table information is accessible from LACP Aggregator datastore.