In l3_learning.py, there is a method in class l3_switch
named _handle_PacketIn
. Now I understand that this event is when a switch contacts controller when it receives a packet corresponding to which it has no entries in its table.
What I don't understand is that here
packet = event.parsed
Now what does packet.next
mean in isinstance(packet.next, ipv4)
?
def _handle_PacketIn (self, event):
dpid = event.connection.dpid
inport = event.port
packet = event.parsed
if not packet.parsed:
log.warning("%i %i ignoring unparsed packet", dpid, inport)
return
if dpid not in self.arpTable:
# New switch -- create an empty table
self.arpTable[dpid] = {}
for fake in self.fakeways:
self.arpTable[dpid][IPAddr(fake)] = Entry(of.OFPP_NONE,
dpid_to_mac(dpid))
if packet.type == ethernet.LLDP_TYPE:
# Ignore LLDP packets
return
if isinstance(packet.next, ipv4):
log.debug("%i %i IP %s => %s", dpid,inport,
packet.next.srcip,packet.next.dstip)
# Send any waiting packets...
self._send_lost_buffers(dpid, packet.next.srcip, packet.src, inport)
# Learn or update port/MAC info
if packet.next.srcip in self.arpTable[dpid]:
if self.arpTable[dpid][packet.next.srcip] != (inport, packet.src):
log.info("%i %i RE-learned %s", dpid,inport,packet.next.srcip)
else:
log.debug("%i %i learned %s", dpid,inport,str(packet.next.srcip))
self.arpTable[dpid][packet.next.srcip] = Entry(inport, packet.src)
# Try to forward
dstaddr = packet.next.dstip
if dstaddr in self.arpTable[dpid]:
# We have info about what port to send it out on...
prt = self.arpTable[dpid][dstaddr].port
mac = self.arpTable[dpid][dstaddr].mac
I think I have figured it out.
packet is entire packet that data-link layer sends to the physical layer. packet.next removes the encapsulation of data-link layer and reveals the IP packet (the packet sent by IP layer to data-link layer). So to get the source MAC address we use packet.src and to get the IP address of the source we use packet.next.srcip
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