Wednesday, October 3, 2018

Ryu measurement based control

ONOS measurement based control describes how real-time streaming telemetry can be used to automatically trigger SDN controller actions. The article uses DDoS mitigation as an example.

This article recreates the demonstration using the Ryu SDN framework and emulating a network using Mininet. Install both pieces of software on a Linux server or virtual machine in order to follow this example.

Start Ryu with the simple_switch and applications loaded:
Note: The simple_switch and ofctl_rest scripts are part of a standard Ryu installation.
This demonstration uses the sFlow-RT real-time analytics engine to process standard sFlow streaming telemetry from the network switches.

Download sFlow-RT:
tar -xvzf sflow-rt.tar.gz
Install the Mininet Dashboard application:
sflow-rt/ sflow-rt mininet-dashboard
The following script, ryu.js, implements the DDoS mitigation function described in the previous article:
var ryu = '';
var controls = {};


setEventHandler(function(evt) {
 // don't consider inter-switch links
 var link = topologyInterfaceToLink(evt.agent,evt.dataSource);
 if(link) return;

 // get port information
 var port = topologyInterfaceToPort(evt.agent,evt.dataSource);
 if(!port) return;

 // need OpenFlow info to create Ryu filtering rule
 if(!port.dpid || !port.ofport) return;

 // we already have a control for this flow
 if(controls[evt.flowKey]) return;

 var [ipdestination,udpsourceport] = evt.flowKey.split(',');
 var msg = {
  match: {

 var resp = http2({
  body: JSON.stringify(msg)

 controls[evt.flowKey] = {,

 logInfo("blocking " + evt.flowKey);

setIntervalHandler(function() {
 var now =;
 for(var key in controls) {
  let rec = controls[key];

  // keep control for at least 10 seconds
  if(now - rec.time < 10000) continue;
  // keep control if threshold still triggered
  if(thresholdTriggered(rec.threshold,rec.agent,rec.metric,key)) continue;

  var resp = http2({
   body: JSON.stringify(rec.msg)

  delete controls[key];

  logInfo("unblocking " + key);
Some notes on the script:
  1. The Ryu is used to add/remove filters that block the DDoS traffic
  2. The udp_reflection flow definition is designed to detect UDP amplification attacks, e.g. DNS amplification attacks
  3. Controls are applied to the switch port where traffic enters the network
  4. The controls structure is used to keep track of state associated with deployed configuration changes so that they can be undone
  5. The intervalHandler() function is used to automatically release controls after 10 seconds - the timeout is short for the purposes of demonstration, in practical deployments the timeout would be much measured in hours
  6. For simplicity, this script is missing the error handling needed for production use.
  7. See Writing Applications for more information.
Run the following command to start sFlow-RT and run the ryu.js script:
./sflow-rt/ -Dscript.file=../ryu.js
We are going to use hping3 to simulate a DDoS attack, so install the software using the following command:
sudo apt install hping3
Next, start Mininet:
sudo mn --custom sflow-rt/extras/ --link tc,bw=10 \
--controller=remote,ip= --topo tree,depth=2,fanout=2
Generate normal traffic between hosts h1 and h3:
mininet> iperf h1 h3
The weathermap view shows the flow crossing the network from switch s2 to s3 via s1.
Generate an attack:
mininet> h1 hping3 --flood --udp -k -s 53 h3
The weathermap view verifies that the attack has been successfully blocked since none of the traffic is seen traversing the network.

The chart at the top of this article shows the iperf test followed by the simulated attack. The top chart shows the top flows entering the network, showing the DNS amplification attack traffic in blue. The middle chart shows traffic broken out by switch port. Here, the blue line shows the attack traffic arriving at switch s2 port s2-eth1 while the red line shows that only a small amount of traffic is forwarded to switch s3 port s3-eth3 before the attack is blocked at switch s2 by the controller.

Mininet with Ryu and sFlow-RT is a great way to rapidly develop and test SDN applications, avoiding the time and expense involved in setting up a physical network. The application is easily moved from the Mininet virtual network to a physical network since it is based on the same industry standard sFlow telemetry generated by physical switches. In this case, using commodity switch hardware to cost effectively detect and filter massive (100's of Gbit/s) DDoS attacks.

Note: Northbound Networks Zodiac GX is an inexpensive gigabit switch that provides a convenient way to transition from an emulated Mininet environment to a physical network handling real traffic.

Monday, October 1, 2018

Systemd traffic marking

Monitoring Linux services describes how the open source Host sFlow agent exports metrics from services launched using systemd, the default service manager on most recent Linux distributions. In addition, the Host sFlow agent efficiently samples network traffic using Linux kernel capabilities: PCAP/BPF, nflog, and ulog.

This article describes a recent extension to the Host sFlow systemd module, mapping sampled traffic to the individual services the generate or consume them. The ability to color traffic by application greatly simplifies service discovery and service dependency mapping; making it easy to see how services communicate in a multi-tier application architecture.

The following /etc/hsflowd.conf file configures the Host sFlow agent, hsflowd, to sampling packets on interface eth0, monitor systemd services and mark the packet samples, and track tcp performance:
sflow {
  collector { ip = }
  pcap { dev = eth0 }
  systemd { markTraffic = on }
  tcp { }
The diagram above illustrates how the Host sFlow agent is able to efficiently monitor and classify traffic. In this case both the Host sFlow agent and an Apache web server are are running as services managed by systemd. A network connection , shown in red, to the HTTP service. In this case, configuring the pcap module to monitor interface eth0 on the server programs a Berkeley Packet Filter (BPF) that randomly samples packets in the Linux kernel and provides copies (shown as the dotted red line) to the Host sFlow agent. In addition, the Host sFlow agent queries systemd to obtain a list of running services and the resources allocated to them. Further Linux kernel tables are queried to identify the network sockets that were opened by each service.

The Host sFlow then attaches an additional record to exported packet samples to indicate the services generating or consuming the packets:
/* Traffic source/sink entity reference */
/* opaque = flow_data; enterprise = 0; format = 2210 */
/* Set Data source to all zeroes if unknown
struct extended_entities {
 sflow_data_source_expanded src_ds;    /* Data Source associated with
                                          packet source */
 sflow_data_source_expanded dst_ds;    /* Data Source associated with
                                          packet destination */
Note: The data source references point to the performance metrics exported by the systemd module, see Monitoring Linux services.

Finally, enabling the tcp module adds delay, retransmit, loss, and reordering information to the sampled packet, see Network performance monitoring.
The screen capture above shows network traffic colored by service name. The chart colors traffic associated with the httpd.service in blue, remote login traffic associated with the sshd.service in red, BGP traffic associated with the bird.service in gold, and traffic to the inmsfd.service in green.

The chart was generated using the open source Flow Trend application running on the sFlow-RT real-time analytics platform. The chart is the result of the following flow definition:
The host: function is used to join information from the sampled flow with telemetry reported for each of the services. Additional keys can be added to the flow definition to break out the traffic by network addresses, quality of service, or any of the many properties reported by sFlow, see Defining Flows for additional information.

Networking on the host has been referred to as the "Goldilocks Zone" because the host provides context that is unavailable in network switches and routers. The sFlow standard defines measurements that network, host, and application entities send in a continuous telemetry stream to analytics software that can combine the data to provide a comprehensive end-to-end view of activity, see sFlow Host Structures.