python - ryu handling packets using a switch after flow was added to switch

python network-programming flowchart flow-control openflow
user2512231 picture user2512231 · Mar 27, 2014 · Viewed 8.7k times · Source

I'm using a Ryu open flow controller switch written in python to monitor packets in my virtual mininet.I have 3 hosts and I'm blocking transportation from host2 to host3 and from host3 to host2. Other packets are added to the switch flow table. My problem is that after a flow is added, if their is a packet between 2 hosts that have a rule in the flow table of the switch, my event doesn't trigger. For example, if the switch saw a packet from host1 to host2 it is legal so the flow is added to the table, but if another packet from host1 to host2 is sent it won't go through the method again. I looked in Ryu guides but didn't find anyhting regarding the case when a flow was already added to the switch flow table. How can I catch the packets?

Thanks in advance.

Here's my code:

import logging
import struct

from ryu.base import app_manager
from ryu.controller import mac_to_port
from ryu.controller import ofp_event
from ryu.controller.handler import MAIN_DISPATCHER
from ryu.controller.handler import set_ev_cls
from ryu.ofproto import ofproto_v1_0
from ryu.lib.mac import haddr_to_str




class SimpleSwitch(app_manager.RyuApp):
OFP_VERSIONS = [ofproto_v1_0.OFP_VERSION]
counterTraffic=0    
def __init__(self, *args, **kwargs):
    super(SimpleSwitch, self).__init__(*args, **kwargs)
    self.mac_to_port = {}

def add_flow(self, datapath, in_port, dst, actions):
    ofproto = datapath.ofproto

    wildcards = ofproto_v1_0.OFPFW_ALL
    wildcards &= ~ofproto_v1_0.OFPFW_IN_PORT
    wildcards &= ~ofproto_v1_0.OFPFW_DL_DST

    match = datapath.ofproto_parser.OFPMatch(
        wildcards, in_port, 0, dst,
        0, 0, 0, 0, 0, 0, 0, 0, 0)

    mod = datapath.ofproto_parser.OFPFlowMod(
        datapath=datapath, match=match, cookie=0,
        command=ofproto.OFPFC_ADD, idle_timeout=0, hard_timeout=0,
        priority=ofproto.OFP_DEFAULT_PRIORITY,
        flags=ofproto.OFPFF_SEND_FLOW_REM, actions=actions)
    datapath.send_msg(mod)

@set_ev_cls(ofp_event.EventOFPPacketIn, MAIN_DISPATCHER)        
def _packet_in_handler(self, ev):

print("Im in main function")
    msg = ev.msg
    datapath = msg.datapath
    ofproto = datapath.ofproto

    dst, src, _eth_type = struct.unpack_from('!6s6sH', buffer(msg.data), 0)

    dpid = datapath.id
    self.mac_to_port.setdefault(dpid, {})

    self.logger.info("packet in %s %s %s %s",
                     dpid, haddr_to_str(src), haddr_to_str(dst),
                     msg.in_port)

if (haddr_to_str(dst) == "00:00:00:00:00:01"):
    print "dst"
    self.counterTraffic +=1

if not ((haddr_to_str(src) == "00:00:00:00:00:02" and  haddr_to_str(dst) =="00:00:00:00:00:03")or (haddr_to_str(src) == "00:00:00:00:00:03" and  haddr_to_str(dst) =="00:00:00:00:00:02")):
        # learn a mac address to avoid FLOOD next time.
    print("after condition")
        self.mac_to_port[dpid][src] = msg.in_port

        if dst in self.mac_to_port[dpid]:
            out_port = self.mac_to_port[dpid][dst]
        else:
                out_port = ofproto.OFPP_FLOOD

            actions = [datapath.ofproto_parser.OFPActionOutput(out_port)]

         # install a flow to avoid packet_in next time
        if out_port != ofproto.OFPP_FLOOD:
                self.add_flow(datapath, msg.in_port, dst, actions)

        out = datapath.ofproto_parser.OFPPacketOut(
        datapath=datapath, buffer_id=msg.buffer_id, in_port=msg.in_port,
                actions=actions)

        datapath.send_msg(out)
    if (haddr_to_str(src) == "00:00:00:00:00:01"):
        print "src"
                self.counterTraffic +=1
    print(self.counterTraffic)


@set_ev_cls(ofp_event.EventOFPPortStatus, MAIN_DISPATCHER)
def _port_status_handler(self, ev):
    msg = ev.msg
    reason = msg.reason
    port_no = msg.desc.port_no

    ofproto = msg.datapath.ofproto
    if reason == ofproto.OFPPR_ADD:
        self.logger.info("port added %s", port_no)
    elif reason == ofproto.OFPPR_DELETE:
        self.logger.info("port deleted %s", port_no)
    elif reason == ofproto.OFPPR_MODIFY:
        self.logger.info("port modified %s", port_no)
    else:
        self.logger.info("Illeagal port state %s %s", port_no, reason)

Answer

This picture This · Apr 4, 2014

I tried to print haddr_to_str(src), haddr_to_str(dst) and got 00:00:00:00:00:03 and ff:ff:ff:ff:ff:ff which is not what I expected. I wanted to get 2 as source and 3 as dest.

The short story is that you're decoding the destination mac address correctly... However, IP must ARP to resolve mac addresses, which is why you see ff:ff:ff:ff:ff:ff... those are just the ARP frames in the ryu controller.

I built a complete controller which, decodes up to the IPv4 layer below...

Updated ryu switch packet decoder

You've been decoding raw structs, but it's much easier to use the ryu Packet library instead of unpacking a raw struct of the packet. This is my very quick replacement of _packet_in_handler(), which just prints out the source and destination mac addresses, as well as the upper layer protocols...

from ryu.lib.packet import packet, ethernet, arp, ipv4
import array

@set_ev_cls(ofp_event.EventOFPPacketIn, MAIN_DISPATCHER)
def _packet_in_handler(self, ev):

    ### Mike Pennington's logging modifications
    ## Set up to receive the ethernet src / dst addresses
    pkt = packet.Packet(array.array('B', ev.msg.data))
    eth_pkt = pkt.get_protocol(ethernet.ethernet)
    arp_pkt = pkt.get_protocol(arp.arp)
    ip4_pkt = pkt.get_protocol(ipv4.ipv4)
    if arp_pkt:
        pak = arp_pkt
    elif ip4_pkt:
        pak = ip4_pkt
    else:
        pak = eth_pkt
    self.logger.info('  _packet_in_handler: src_mac -> %s' % eth_pkt.src)
    self.logger.info('  _packet_in_handler: dst_mac -> %s' % eth_pkt.dst)
    self.logger.info('  _packet_in_handler: %s' % pak)
    self.logger.info('  ------')
    src = eth_pkt.src  # Set up the src and dst variables so you can use them
    dst = eth_pkt.dst
    ## Mike Pennington's modifications end here

    
    msg = ev.msg
    datapath = msg.datapath
    ofproto = datapath.ofproto

    dpid = datapath.id
    self.mac_to_port.setdefault(dpid, {})

    # learn a mac address to avoid FLOOD next time.
    self.mac_to_port[dpid][src] = msg.in_port

    if dst in self.mac_to_port[dpid]:
        out_port = self.mac_to_port[dpid][dst]
    else:
        out_port = ofproto.OFPP_FLOOD

    actions = [datapath.ofproto_parser.OFPActionOutput(out_port)]

    # install a flow to avoid packet_in next time
    if out_port != ofproto.OFPP_FLOOD:
        self.add_flow(datapath, msg.in_port, dst, actions)

    out = datapath.ofproto_parser.OFPPacketOut(
        datapath=datapath, buffer_id=msg.buffer_id, in_port=msg.in_port,
        actions=actions)
    datapath.send_msg(out)

Now, whenever an ethernet packet is sent, you'll see this inside your mininet session...

  _packet_in_handler: src_mac -> 00:00:00:00:00:03
  _packet_in_handler: dst_mac -> 33:33:00:00:00:02
  _packet_in_handler: ethernet(dst='33:33:00:00:00:02',ethertype=34525,src='00:00:00:00:00:03')
  ------

ARP packets look like this...

  _packet_in_handler: src_mac -> 00:00:00:00:00:01
  _packet_in_handler: dst_mac -> ff:ff:ff:ff:ff:ff
  _packet_in_handler: arp(dst_ip='10.0.0.2',dst_mac='00:00:00:00:00:00',hlen=6,hwtype=1,opcode=1,plen=4,proto=2048,src_ip='10.0.0.1',src_mac='00:00:00:00:00:01')
  ------

Demo

Assume I saved the modified code above (including other parts of your source) as ne_question.py.

root@mininet-vm:/home/mininet# ryu-manager ne_question.py &
                 [1] 14073
loading app ne_question.py
loading app ryu.controller.ofp_handler
instantiating app ryu.controller.ofp_handler of OFPHandler
instantiating app ne_question.py of SimpleSwitch

root@mininet-vm:/home/mininet#
  • Next I build the switch topology, as you mentioned in your comment
root@mininet-vm:/home/mininet# mn --topo single,3 --mac --switch ovsk --controller remote
*** Creating network
*** Adding controller
*** Adding hosts:
h1 h2 h3
*** Adding switches:
s1
*** Adding links:
(h1, s1) (h2, s1) (h3, s1)
*** Configuring hosts
h1 h2 h3
*** Starting controller
*** Starting 1 switches
s1
*** Starting CLI:
mininet>   _packet_in_handler: src_mac -> 00:00:00:00:00:02
  _packet_in_handler: dst_mac -> 33:33:00:00:00:02
  _packet_in_handler: ethernet(dst='33:33:00:00:00:02',ethertype=34525,src='00:00:00:00:00:02')
  ------
  _packet_in_handler: src_mac -> 00:00:00:00:00:01
  _packet_in_handler: dst_mac -> 33:33:00:00:00:02
  _packet_in_handler: ethernet(dst='33:33:00:00:00:02',ethertype=34525,src='00:00:00:00:00:01')
  ------
  _packet_in_handler: src_mac -> 00:00:00:00:00:03
  _packet_in_handler: dst_mac -> 33:33:00:00:00:02
  _packet_in_handler: ethernet(dst='33:33:00:00:00:02',ethertype=34525,src='00:00:00:00:00:03')
  ------
  • Finally, I run the web server, and try to pull a page... notice that ARPs are sent to resolve the destination address of the http GET. The destination address of the ARPs are ff:ff:ff:ff:ff:ff. BTW, if you change the wget to h2 wget h1, everything works correctly...
mininet> h1 python -m SimpleHTTPServer 80 &
mininet> h2 wget -O - h1
--2014-03-28 04:22:25--  http://10.0.0.1/
Connecting to 10.0.0.1:80...   _packet_in_handler: src_mac -> 00:00:00:00:00:02
  _packet_in_handler: dst_mac -> ff:ff:ff:ff:ff:ff
  _packet_in_handler: arp(dst_ip='10.0.0.1',dst_mac='00:00:00:00:00:00',hlen=6,hwtype=1,opcode=1,plen=4,proto=2048,src_ip='10.0.0.2',src_mac='00:00:00:00:00:02')
  ------
--2014-03-28 04:00:58--  http://10.0.0.1/
Connecting to 10.0.0.1:80...   _packet_in_handler: src_mac -> 00:00:00:00:00:02
  _packet_in_handler: dst_mac -> 00:00:00:00:00:01
  _packet_in_handler: ipv4(csum=33886,dst='10.0.0.1',flags=2,header_length=5,identification=41563,offset=0,option=None,proto=6,src='10.0.0.2',tos=0,total_length=60,ttl=64,version=4)
  ------
  _packet_in_handler: src_mac -> 00:00:00:00:00:01
  _packet_in_handler: dst_mac -> 00:00:00:00:00:02
  _packet_in_handler: ipv4(csum=9914,dst='10.0.0.2',flags=2,header_length=5,identification=0,offset=0,option=None,proto=6,src='10.0.0.1',tos=0,total_length=60,ttl=64,version=4)
  ------
connected.
HTTP request sent, awaiting response...   _packet_in_handler: src_mac -> 00:00:00:00:00:02
  _packet_in_handler: dst_mac -> 00:00:00:00:00:01
  _packet_in_handler: ipv4(csum=33893,dst='10.0.0.1',flags=2,header_length=5,identification=41564,offset=0,option=None,proto=6,src='10.0.0.2',tos=0,total_length=52,ttl=64,version=4)
  ------
  _packet_in_handler: src_mac -> 00:00:00:00:00:02
  _packet_in_handler: dst_mac -> 00:00:00:00:00:01
  _packet_in_handler: ipv4(csum=33784,dst='10.0.0.1',flags=2,header_length=5,identification=41565,offset=0,option=None,proto=6,src='10.0.0.2',tos=0,total_length=160,ttl=64,version=4)
  ------
  _packet_in_handler: src_mac -> 00:00:00:00:00:01
  _packet_in_handler: dst_mac -> 00:00:00:00:00:02
  _packet_in_handler: ipv4(csum=61034,dst='10.0.0.2',flags=2,header_length=5,identification=14423,offset=0,option=None,proto=6,src='10.0.0.1',tos=0,total_length=52,ttl=64,version=4)
  ------
  _packet_in_handler: src_mac -> 00:00:00:00:00:01
  _packet_in_handler: dst_mac -> 00:00:00:00:00:02
  _packet_in_handler: ipv4(csum=61016,dst='10.0.0.2',flags=2,header_length=5,identification=14424,offset=0,option=None,proto=6,src='10.0.0.1',tos=0,total_length=69,ttl=64,version=4)
  ------
  _packet_in_handler: src_mac -> 00:00:00:00:00:01
  _packet_in_handler: dst_mac -> 00:00:00:00:00:02
  _packet_in_handler: ipv4(csum=60037,dst='10.0.0.2',flags=2,header_length=5,identification=14425,offset=0,option=None,proto=6,src='10.0.0.1',tos=0,total_length=1047,ttl=64,version=4)
  ------
200 OK
Length: 858 [text/html]
Saving to: `STDOUT'
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html>
<title>Directory listing for /</title>
<body>
<h2>Directory listing for /</h2>
<hr>
<ul>
<li><a href=".bash_history">.bash_history</a>
<li><a href=".bash_logout">.bash_logout</a>
<li><a href=".bashrc">.bashrc</a>
<li><a href=".cache/">.cache/</a>
<li><a href=".gitconfig">.gitconfig</a>
<li><a href=".profile">.profile</a>
<li><a href=".rnd">.rnd</a>
<li><a href=".wireshark/">.wireshark/</a>
<li><a href="install-mininet-vm.sh">install-mininet-vm.sh</a>
<li><a href="mininet/">mininet/</a>
<li><a href="ne_question.py">ne_question.py</a>
<li><a href="ne_question.pyc">ne_question.pyc</a>
<li><a href="of-dissector/">of-dissector/</a>
<li><a href="oflops/">oflops/</a>
<li><a href="oftest/">oftest/</a>
<li><a href="openflow/">openflow/</a>
<li><a href="pox/">pox/</a>
</ul>
<hr>
</body>
</html>

     0K                                                       100%  161M=0s

2014-03-28 04:00:58 (161 MB/s) - written to stdout [858/858]

  _packet_in_handler: src_mac -> 00:00:00:00:00:02
mininet>   _packet_in_handler: dst_mac -> 00:00:00:00:00:01
  _packet_in_handler: ipv4(csum=33891,dst='10.0.0.1',flags=2,header_length=5,identification=41566,offset=0,option=None,proto=6,src='10.0.0.2',tos=0,total_length=52,ttl=64,version=4)
  ------
  _packet_in_handler: src_mac -> 00:00:00:00:00:02
  _packet_in_handler: dst_mac -> 00:00:00:00:00:01
  _packet_in_handler: ipv4(csum=33890,dst='10.0.0.1',flags=2,header_length=5,identification=41567,offset=0,option=None,proto=6,src='10.0.0.2',tos=0,total_length=52,ttl=64,version=4)
  ------
  _packet_in_handler: src_mac -> 00:00:00:00:00:02
  _packet_in_handler: dst_mac -> 00:00:00:00:00:01
  _packet_in_handler: ipv4(csum=33889,dst='10.0.0.1',flags=2,header_length=5,identification=41568,offset=0,option=None,proto=6,src='10.0.0.2',tos=0,total_length=52,ttl=64,version=4)
  ------
  _packet_in_handler: src_mac -> 00:00:00:00:00:01
  _packet_in_handler: dst_mac -> 00:00:00:00:00:02
  _packet_in_handler: ipv4(csum=9922,dst='10.0.0.2',flags=2,header_length=5,identification=0,offset=0,option=None,proto=6,src='10.0.0.1',tos=0,total_length=52,ttl=64,version=4)
  ------

mininet>
mininet>

Related questions

Ping a site in Python?

How do I ping a website or IP address with Python?

Read More
How to measure server response time for Python requests POST-request?

I create requests POST-requests like this, where I specify timeout threshold: response = requests.post(url, data=post_fields, timeout=timeout) However, to determine a "good" threshold value, I would like to benchmark the server response time in advance. How do …

Read More
How to copy a file from a network share to local disk with variables?

If I use the following line: shutil.copyfile(r"\\mynetworkshare\myfile.txt","C:\TEMP\myfile.txt") everything works fine. However, what I can't seem to figure out is how to use a variable with the network share path, because I …

Read More