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ARP Proxy example

This exercise helps to understand, generating packets from the controller. This is ARP Proxy application. This application answers the ARP requests(instead of forwarding the ARP broadcasts to all hosts)

Objective

This Application act as ARP Proxy. It captures the ARP Packets, builds the ARP response and send it to the Src.

code changes :

  1. include the lib
from ryu.lib.packet import arp
  1. define your table
arp_table = {"10.0.0.1": "00:00:00:00:00:01",
             "10.0.0.2": "00:00:00:00:00:02",
             "10.0.0.3": "00:00:00:00:00:03",
             "10.0.0.4": "00:00:00:00:00:04"
             }
  1. Write your arp proxy function.
    def arp_process(self, datapath, eth, a, in_port):
        r = arp_table.get(a.dst_ip)
        if r:
            self.logger.info("Matched MAC %s ", r)
            arp_resp = packet.Packet()
            arp_resp.add_protocol(ethernet.ethernet(ethertype=eth.ethertype,
                                  dst=eth.src, src=r))
            arp_resp.add_protocol(arp.arp(opcode=arp.ARP_REPLY,
                                  src_mac=r, src_ip=a.dst_ip,
                                  dst_mac=a.src_mac,
                                  dst_ip=a.src_ip))

            arp_resp.serialize()
            actions = []
            actions.append(datapath.ofproto_parser.OFPActionOutput(in_port))
            parser = datapath.ofproto_parser  
            ofproto = datapath.ofproto
            out = parser.OFPPacketOut(datapath=datapath, buffer_id=ofproto.OFP_NO_BUFFER,
                                  in_port=ofproto.OFPP_CONTROLLER, actions=actions, data=arp_resp)
            datapath.send_msg(out)
            self.logger.info("Proxied ARP Response packet")
  1. In the packet handler function, if it arp packet, call the arp_proxy function.
        # Check whether is it arp packet
        if eth.ethertype == ether_types.ETH_TYPE_ARP:
            self.logger.info("Received ARP Packet %s %s %s ", dpid, src, dst)
            a = pkt.get_protocol(arp.arp)
            self.arp_process(datapath, eth, a, in_port)
            return

Testing

  1. Run your topology ( Linear topology)
sudo mn --controller=remote,ip=127.0.0.1 --mac  --switch=ovsk,protocols=OpenFlow13 --topo=linear,4
  1. Run the RYU controller application
ryu-manager ex8_arp_proxy.py
  1. run tcpdump in the nodes

In mininet

xterm h1
xterm h2

in the xterminal,

tcpdump -i any -v
  1. ping host1 to host2 from the mininet
h1 ping h2
  1. check the tcpdump output

References:

https://github.com/osrg/ryu/blob/master/ryu/lib/packet/arp.py