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The Path Daemon application is responsible for pushing end-to-end flows for all ARP and IPv4
flow misses that arrive at the controller. By default, Path Daemon is responsible for Layer-2
forwarding only. This component depends on other network service components like the Node
manager and the Path Selection manager.
Path Daemon does the following:
Registers with the controller as a Director. Directors are allowed to send a packet out.
Registers for ARP packets and IPv4 packets.
Uses the Node Manager to get the end hosts corresponding to the source and destination
MAC addresses and the datapaths to which these hosts are connected. It makes use of the
Path Selection manager to get the end-to-end shortest path between the source and
destination hosts. It makes use of the controller to push flows to the datapaths. The flowchart
in
Figure 2
Path Daemon uses the following match fields when pushing a flow-mod. These match fields
have been chosen so that the flow modules are pushed on hardware tables in both
ProVision-based and Comware-based switches.
◦
Ether type: OFPXMT_OFB_ETH_TYPE
◦
Source MAC or IP address: OFPXMT_OFB_ETH_SRC or OFPXMT_OFB_IPV4_SRC
◦
Destination MAC or IP address: OFPXMT_OFB_ETH_DST or OFPXMT_OFB_IPV4_DST
◦
Input port: OFPXMT_OFB_IN_PORT
Path Daemon also registers for Port Status Down messages. When such messages are
received, Path Daemon removes all flows configured for the impacted port, thereby causing
the PACKET_IN messages to again come to the controller.
Operational notes
The Path Daemon:
Does not handle multicast or broadcast traffic
Does not configure the reverse path along with the forward path
Drops packets from sources that the controller has not learned
Floods packets when their destinations are not known
Does not support fast-failover
Performance is topology-dependent, recommended for 100-200 node environments, and
can degrade when there is a larger number of nodes
18
Understanding the controller architecture
provides more details of its operation.
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