Reference Guide

OpenFlow Link Discovery
OpenFlow Link Discovery pushes flow-mods to controlled devices and listens for PACKET_IN
messages in order to discover links on the controlled network. When hybrid.mode=true in the
ControllerManager configuration, OpenFlow Link Discovery will push a flow to controlled devices
which steals all controller-generated link discovery packets to the controller. The controller-
generated link discovery packets use a non-standard protocol (BDDP), which utilizes a payload
format similar to LLDP. All discovery packets generated by the controller will be sent to either a link-
local MAC address (to discover direct links) or a multicast MAC address (to discover multi-hop
links). The multicast MAC address used for link discovery is 01:1B:78:E9:7B:CD. When the
controller injects a discovery packet, the packet content contains the device ID which introduces
the packet to the controlled network.
OpenFlow Link Discovery listens for PACKET_IN messages which contain the BDDP protocol. Each
discovery packet has the source device ID embedded within its payload, and the destination
device can be derived from the PACKET_IN message. This allows the OpenFlow Link Discovery
application to populate the link table with information it learns from such received packets. Note
that since these PACKET_IN messages are for controller-generated link discovery packets, no
corresponding PACKET_OUT will be sent back to the device which sent the PACKET_IN.
OpenFlow Link Discovery periodically injects discovery packets into the controlled network to
refresh the contents of the link table. Any links which are not refreshed at this periodic interval are
considered to be invalid and are removed from the link table. Additionally, network events such as
a port going down or a device going offline will cause relevant links to be removed.
Topology Manager
Topology Manager provides topology information of the control domain. It also facilitates shortest
path traversals through the control domain by way of computing low cost next hops between any
two elements in the control domain. Topology Manager computes the clusters and broadcast tree
to avoid loops and broadcast storms.
•
Provides a list of discovered ports on a given switch.
•
Indicates whether a switch port is an edge port (connection point) or part of a link.
•
indicate whether a port is in a blocked or open state by determining whether ingress
broadcast traffic is allowed through the port
•
Verifies if a path exists between two nodes.
•
Identifies the shortest path between two nodes.
•
Provides enumeration of the grouping of switches into clusters of strongly connected nodes.
•
For a given switch provides cluster details it belongs.
Topology manager provides notifications to subscribed applications on changes in its broadcast
tress and cluster, intelligent applications can be developed which takes proactive measures by way
of subscribing for these topology re-computed notifications
Services published by Topology Service
•
Given two switches (s1, s2) this can indicate if they can be reached via directly connected
paths
240