[Ryu-devel] Understanding ARP Request Handling by Ryu controller

[Ruchika L. <h20...@pi...>]

Hello,

I am a newbie to Ryu SDN Controller. I am trying to understand the handling
of ARP Requests and generation of ARP Replies by RYU controller. As per my
understanding:

1.When ARP request arrives at the switch, there is no flow registrations in
switch to forward ARP Packets.
2. ARP Packets are then sent to the controller.
3. Now at the controller side, I found this code for handling the ARP
requests:
*def _handle_arp(self, datapath, port, pkt_ethernet, pkt_arp):*
*if pkt_arp.opcode != arp.ARP_REQUEST:*
*return*
*pkt = packet.Packet()*
*pkt.add_protocol(ethernet.ethernet(ethertype=pkt_ethernet.ethertype,*
*dst=pkt_ethernet.src,*
*src=self.hw_addr))*
*pkt.add_protocol(arp.arp(opcode=arp.ARP_REPLY,*
*src_mac=self.hw_addr,*
*src_ip=self.ip_addr,*
*dst_mac=pkt_arp.src_mac,*
*dst_ip=pkt_arp.src_ip))*
*self._send_packet(datapath, port, pkt)*
 where it is constructing ARP replies. Now my question is, when and where
is the mapping between IP and MAC stored at the controller side. When does
the controller figure out the mapping, at ARP request or is it known
already to the controller? And which data structure is used to store this
mapping?

** If you can point out the exact structure to represent ARP Cache, it
would be great**

Thank you



Ruchika Luthra