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RYU Part2:

In this part , we are going to start writing the sample RYU applications step by step.

Base Rule for beginners: Please copy the example application file and modify as per your needs.

In this ryu exercises, i am going to use Openflow 1.3 Version, and use simple_switch_13.py as example program to start with.

RYU Application overview:

Step1 : Import the base classes / library

from ryu.base import app_manager

from ryu.controller import ofp_event
from ryu.controller.handler import CONFIG_DISPATCHER, MAIN_DISPATCHER
from ryu.controller.handler import set_ev_cls

from ryu.ofproto import ofproto_v1_3

from ryu.lib.packet import packet
from ryu.lib.packet import ethernet
from ryu.lib.packet import ether_types

app_manager : main entry point for the application.

set_ev_cls, ofp_event, Dispatcher : used for capturing openflow event, when the openflow packet received

ofproto_v1_3 : Specifies which Openflow version to be used.

packet, ethernet, ether_types : packet processing library

step2: Define your application class (derived from app_manager) and write the base stuff:

class SimpleSwitch13(app_manager.RyuApp):

sets the openflow version

 OFP_VERSIONS = [ofproto_v1_3.OFP_VERSION]
  1. define the constructor .
def __init__(self, *args, **kwargs):
super(SimpleSwitch13, self).__init__(*args, **kwargs)

step3: Handle the relavent Openflow events (when the openflow feature request message received, When the openflow packet in message received):

In the Event handler, write your application logic.

How to Implement Openflow L2 Switch in RYU :

  1. mac_to_port dictionary to store the mac table.

  2. In Switch Feature Request Event handler Insert table miss entry (using add_flow function). Table Miss entry flow: Match all packets, priority 0, forward it to controller port.

  3. In Packet_In Handler, Inspect the incoming packet, Update the mac_to_port dictionary wth "soruce mac" and " incoming port" Check the destination mac is present in the mac_to_port dictionary. if present, match = inport, srcmac, dstmac action = forward ot the port number Add a flow (with match, action). else action = flood a packet call packet out with action.

Execute the Openflow L2 Switch :

ryu-manager simple_switch_13.py

Run the Mininet Topology

sudo mn --controller=remote,ip=127.0.0.1 --mac -i 10.1.1.0/24 --switch=ovsk,protocols=OpenFlow13 --topo=linear,4

Check the output.

References

https://en.wikipedia.org/wiki/OpenFlow

http://ryu.readthedocs.io/en/latest/

https://osrg.github.io/ryu/resources.html

https://github.com/osrg/ryu/tree/master/ryu