Thursday, November 16, 2017

RESTful control of Cumulus Linux ACLs

The diagram above shows how the Cumulus Linux 3.4 HTTP API can be extended to include the functionality described in REST API for Cumulus Linux ACLs. Fast programmatic control of Cumulus Linux ACLs addresses a number of interesting use cases, including: DDoS mitigationElephant flow marking, and Triggered remote packet capture using filtered ERSPAN.

The Github pphaal/acl_server project INSTALL page describes how to install the acl_server daemon and configure the NGINX web server front end for the Cumulus Linux REST API to include the acl_server functions. The integration ensures that the same access controls configured for the REST API apply to the acl_server functions, which appear under the /acl/ path.

The following examples demonstrate the REST API.

Create an ACL

curl -X PUT -H 'Content-Type:application/json' --data '["[iptables]","-A FORWARD --in-interface swp+ -d -p udp --sport 53 -j DROP"]' -k -u 'cumulus:CumulusLinux!'
ACLs are sent as a JSON encoded array of strings. Each string will be written as a line in a file stored under /etc/cumulus/acl/policy.d/ - See Cumulus Linux: Netfilter - ACLs. For example, the rule above will be written to the file 50rest-ddos1.rules with the following content:
-A FORWARD --in-interface swp+ -d -p udp --sport 53 -j DROP
This iptables rule blocks all traffic from UDP port 53 (DNS) to host This is the type of rule that might be inserted to block a DNS amplification attack.

Retrieve an ACL

curl -k -u 'cumulus:CumulusLinux!'
Returns the result:
 "-A FORWARD --in-interface swp+ -d -p udp --sport 53 -j DROP"

List ACLs

curl -k -u 'cumulus:CumulusLinux!'
Returns the result:

Delete an ACL

curl -X DELETE -k -u 'cumulus:CumulusLinux!'

Delete all ACLs

curl -X DELETE -k -u 'cumulus:CumulusLinux!'
Note: this doesn't delete all the ACLs, just the ones created using the REST API. All default ACLs or manually created ACLs are inaccessible through the REST API.


The acl_server batches and compiles changes after the HTTP requests complete. Batching has the benefit of increasing throughput and reducing request latency, but makes it difficult to track compilation errors since they are reported later. The acl_server catches the output and status when running cl-acltool and attaches an HTTP Warning header to subsequent requests to indicate that the last compilation failed:
HTTP/1.1 200 OK
Server: nginx/1.6.2
Date: Thu, 16 Nov 2017 21:38:03 GMT
Content-Type: application/json
Transfer-Encoding: chunked
Connection: keep-alive
Keep-Alive: timeout=300
Accept: application/json
Warning: 199 - "check lasterror"
The output of cl-acltool can be retrieved:
curl -k -u 'cumulus:CumulusLinux!'
Returns the result:
{"returncode": 255, "lines": [...]}
The REST API is intended to be used by automation systems and so syntax problems with the ACLs they generate should be rare and are the result of a software bug. A controller using this API should check responses for the presence of the last error Warning, log the lasterror information so that the problem can be debugged, and finally delete all the rules created through the REST API to restore the system to its default state.

While this REST API could be used as a convenient way to manually push an ACL to a switch, the API is intended to be part of automation solutions that combine real-time traffic analytics with automated control. Cumulus Linux includes standard sFlow measurement support, delivering real-time network wide visibility to drive solutions that include: DDoS mitigation, enforcing black lists, marking large flows, ECMP load balancing, packet brokers etc.

The acl_server functionality demonstrates the value of the open Linux environment exposed by Cumulus Linux, making it easy to extend the platform using standard Linux tools in order to address operational requirements. Download the free Cumulus Linux VX virtual machine to try these examples yourself.

Monday, November 13, 2017

Real-time WiFi heat map

Real-time Wifi-Traffic Heatmap (source code GitHub: cod3monk/showfloor-heatmap) displays real-time WiFi traffic from SC17 (The International Conference for High Performance Computing, Networking, Storage and Analysis, November 12-17, 2017). Click on the link to see live data.

The Cisco Wireless access points in the conference network don't currently support sFlow, however, the access points are connected to Juniper EX switches which stream sFlow telemetry to an instance of sFlow-RT analytics software that provides real-time usage metrics for the heat map.

Wireless describes the additional visibility delivered by sFlow capable wireless access points, including: air time, channel, retransmissions, receive / transmit speeds, power, signal to noise ratio, etc. With sFlow enabled wireless access points, additional information could be layered on the heat map. The web site lists network products and vendors that support the sFlow standard.

Tuesday, October 17, 2017

Arista EOS CloudVision

Arista EOS® CloudVision® provides a centralized point of visibility, configuration and control for Arista devices. The CloudVision controller is available as a virtual machine or physical appliance.

Fabric Visibility on Arista EOS Central describes how to use industry standard sFlow instrumentation in Arista switches to deliver real-time flow analytics. This article describes the steps needed to integrate flow analytics into CloudVision.

Log into the CloudVision node and run the following script as root:
# Install Fabric View on CloudVision Portal (CVP)

VER=`wget -qO -`
rpm --nodeps -ivh sflow-rt-$VER.noarch.rpm
/usr/local/sflow-rt/ sflow-rt fabric-view

ln -s /cvpi/jdk/bin/java /usr/bin/java

sed -i '/^# http.hostname=/s/^# //' /usr/local/sflow-rt/conf.d/sflow-rt.conf
echo "http.html.redirect=./app/fabric-view/html/" >> /usr/local/sflow-rt/conf.d/sflow-rt.conf

cat <<EOT > /etc/nginx/conf.d/locations/sflow-rt.https.conf
location /sflow-rt/ {
  auth_request /aeris/auth;
  proxy_buffering off;
  proxy_set_header X-Forwarded-For \$proxy_add_x_forwarded_for;
  proxy_set_header X-Forwarded-Prefix /sflow-rt/;
  proxy_set_header Host \$host;
  proxy_pass http://localhost:8008/;
  proxy_redirect ~^http://[^/]+(/.+)\$ /sflow-rt\$1;

systemctl restart nginx.service

firewall-cmd --zone public --add-port=6343/udp --permanent
firewall-cmd --reload

systemctl enable sflow-rt.service
systemctl start sflow-rt.service

chmod +x

echo "configure and run"
Edit the script to specify CVP_USER and CVP_PASSWORD (and EAPI_USER and EAPI_PASSWORD if they differ). Now run the script to discover the physical topology and post it to Fabric View:
Note: The script needs to be run any time the physical topology changes, or you can run the script periodically using cron.

Flow analytics requires sFlow to be enabled on all the switches, sending the data to the CloudVision node. This can be accomplished using a CloudVision configlet to push the configuration to switches. For example the following configuration enables sFlow on all switch ports and sends the data to CloudVision node
sflow sample 20000
sflow polling-interval 30
sflow destination
sflow source-interface Management1
sflow run
Optionally, follow the steps in Arista EOS telemetry to enhance the sFlow telemetry stream from the switches with detailed CPU, memory, disk, and host network statistics.

Finally, access the Fabric View web interface at https://cloudvision/sflow-rt/ using your CloudVision login credentials.
Fabric View is an open source application running on top of the sFlow-RT analytics engine. The Fabric View software can easily be modified to add new capabilities, e.g. Black hole detection.

A number of applications are available for sFlow-RT. Writing Applications describes how to use sFlow-RT's APIs to extend or modify existing applications or develop new applications. In addition, there are also many sFlow-RT related articles on this blog. For example, Arista eAPI describes how to automatically push controls based on flow measurements, describing automated DDoS mitigation as a use case. Other use cases include: traffic engineering, traffic accounting, anomaly detection, intrusion detection, FIB optimization, targeted packet capture etc.

Wednesday, September 27, 2017

Real-time visibility and control of campus networks

Many of the examples on this blog describe network visibility driven control of data center networks. However, campus networks face many similar challenges and the availability of industry standard sFlow telemetry and RESTful control APIs in campus switches make it possible to apply feedback control.

HPE Aruba has an extensive selection of campus switches that combine programmatic control via a REST API with hardware sFlow support:
  • Aruba 2530 
  • Aruba 2540 
  • Aruba 2620
  • Aruba 2930F
  • Aruba 2930M
  • Aruba 3810
  • Aruba 5400R
  • Aruba 8400
 This article presents an example of implementing quota controls using HPE Aruba switches.
Typically, a small number of hosts are responsible for the majority of traffic on the network: identifying those hosts, and applying controls to their traffic to prevent them from unfairly dominating, ensures fair access to all users.

Peer-to-peer protocols (P2P) pose some unique challenges:
  • P2P protocols make use of very large numbers of connections in order to quickly transfer data. The large number of connections allows a P2P user to obtain a disproportionate amount of network bandwidth; even a small number of P2P users (less than 0.5% of users) can consume over 90% of the network bandwidth.
  • P2P protocols (and users) are very good at getting through access control lists (acl) by using non-standard ports, using port 80 (web) etc. Trying to maintain an effective filter to identify P2P traffic is a challenge and the resulting complex rule sets consume significant resources in devices attempting to perform classification.
In this example, all switches are configured to stream sFlow telemetry to an instance of the sFlow-RT real-time sFlow analyzer running a quota controller. When a host exceeds its traffic quota, a REST API call is made to the host's access switch, instructing the switch to mark the host's traffic as low priority. Marking the traffic ensures that if congestion occurs elsewhere in the network, typically on the Internet access links, priority queuing will cause marked packets can be dropped, reducing the bandwidth consumed by the marked host. The quota controller continues to monitor the host and the marking action is removed when the host's traffic returns to acceptable levels.

A usage quota is simply a limit on the amount of traffic that a user is allowed to generate in a given amount of time. Usage quotas have a number of attributed that make them an effective means of managing P2P activity:
  • A simple usage quota is easy to maintain and enforce and encourages users to be more responsible in their use of shared resources.
  • Since quota based controls are interested in the overall amount of traffic that a host generates and not the specific type of traffic, they don't encourage users to tailor P2P application setting to bypass access control rules and so their traffic is easier to monitor.
  • A quota system can be implemented using standard network hardware, without the addition of a "traffic shaping" appliance that can become a bottleneck and point of failure.
The following quota.js script implements the quota controller functionality:
var user = 'manager';
var password = 'manager';
var scheme = 'http://';
var mbps = 10;
var interval = 10;
var timeout = 20;
var dscp = '10';
var groups = {'ext':[''],'inc':[''],'exc':['']};

function runCmd(agent,cmd) {
  var headers = {'Content-Type':'application/json','Accept':'application/json'};
  // create session
  var auth = http2({
    body: JSON.stringify({userName:user, password:password})

  // make request
  var resp = http2({
    body: JSON.stringify({cmd:cmd})
  var result = base64Decode(JSON.parse(resp.body).result_base64_encoded);

  // end session
  var end = http2({
  return result;


setFlow('src', {

setThreshold('quota', {
  byFlow: true,

var controls = {};
setEventHandler(function(evt) {
  var ip = evt.flowKey;
  if(controls[ip]) return;

  var agent = evt.agent;
  var ds = evt.dataSource;
  controls[ip] = {agent:agent,ds:ds,};
  logInfo('mark '+ip+' agent '+agent);
  try { runCmd(agent,'qos device-priority '+ip+' dscp '+dscp); }
  catch(e) { logWarning('runCmd error ' + e); }
}, ['quota']);

setIntervalHandler(function() {
  for(var ip in controls) {
    var ctl = controls[ip];
    if(thresholdTriggered('quota',ctl.agent,ctl.ds+'.src',ip)) continue;

    logInfo('unmark '+ip+' agent '+ctl.agent);
    try { runCmd(ctl.agent,'no qos device-priority '+ip); }
    catch(e) { logWarning('runCmd error ' + e); }
    delete controls[ip];
Some notes on the script:
  • Writing Applications provides an overview of the sFlow-RT scripting API.
  • HPE ArubaOS-Switch REST API and JSON Schema Reference Guide 16.03 describes the REST API calls in the runCmds() function.
  • The groups variable defines groups of IP addresses, identifying external addresses (ext), addresses included as candidates for the quota controller (inc), and addresses excluded from quota controls (exc).
  • Defining Flows describes the arguments to the setFlow() function. In this case, calculating a 10 second moving average of traffic from local sources (inc) to external destinations (ext).
  • The setThreshold() function creates a threshold that triggers if the moving average of traffic from an address exceeds 10Mbit/s. The thresholds are only applied to 10M, 100M and 1G access ports, ensuring that controls are only applied to access layer switches and not to 10G ports on aggregation and core switches.
  • The setEventHandler() function processes the events, keeping track of existing controls and implementing new DSCP marking rules.
  • The setIntervalHandler() function runs periodically and removes marking rules when they are not longer required (after the threshold timeout has expired).
  • The ArubaOS commands to add / remove DSCP marking for the host are highlighted in blue.
The easiest way to try out the script is to use Docker to run sFlow-RT:
docker run -v $PWD/cli.js:/sflow-rt/quota.js -e "RTPROP=-Dscript.file=quota.js" -p 6343:6343/udp -p 8008:8008 sflow/sflow-rt
2017-09-27T02:32:14+0000 INFO: Listening, sFlow port 6343
2017-09-27T02:32:14+0000 INFO: Listening, HTTP port 8008
2017-09-27T02:32:14+0000 INFO: quota.js started
2017-09-27T02:33:53+0000 INFO: mark agent
2017-09-27T02:34:25+0000 INFO: unmark agent
The output indicates that a control marking traffic from was added to edge switch and removed just over 30 seconds later.
The screen capture using Flow Trend to monitor the core switches shows the controller in action. The marking rule is added as soon as traffic from exceeds the 10Mbps quota for 10 seconds (the DSCP marking shown in the chart changes from red be(0) to blue af11(10)). The marking rule is removed once the traffic returns to normal.
The quota settings in the demonstration were aggressive. In practice the threshold settings would be higher and the timeouts longer in order to minimize control churn. The trend above was collected from a university network of approximately 20,000 users that implemented a similar control scheme. In this case, the quota controller was able to consistently mark 50% of the traffic as low priority. Between 10 and 20 controls were in place at any given time and the controller made around 10 control changes an hour (adding or removing a control). During busy periods, congestion on the campus Internet access links was eliminated since marked traffic could be discarded when necessary.

Implementing usage quotas is just one example of applying measurement based control to a campus network. Other interesting applications include:
Real-time measurement and programmatic APIs are becoming standard features of campus switches, allowing visibility driven automatic control to adapt the network to changing network demands and security threats.

Wednesday, September 20, 2017

Flow Trend

The open source sflow-rt/flow-trend project displays a real-time trend chart of network traffic that updates every second. Defining Flows describes how to break out traffic by different traffic attributes, including: addresses, ports, VLANs, protocols, countries, DNS names, etc.
docker run -p 6343:6343/udp -p 8008:8008 sflow/flow-trend
The simplest way to run the software is using the docker. Configure network devices to send standard sFlow telemetry to Flow Trend. Access the web user interface on port 8008.

Sunday, September 10, 2017

Real-time traffic visualization using Netflix Vizceral

The open source sflow-rt/vizceral project demonstrates how real-time sFlow network telemetry can be presented using Netflix Vizceral. The central dot represents the Internet (all non-local addresses). The surrounding dots represents addresses grouped into sites, data centers, buildings etc. The animated particle flows represent packet flows with colors indicating packet type: TCP/UDP shown in blue, ICMP shown in yellow, and all other traffic in red.
Click on a node to zoom in to show packets flowing up and down the protocol stack. Press the ESC key to unzoom.

The simplest way to run the software is to use the pre-built Docker image:
docker run -p 6343:6343/udp -p 8008:8008 sflow/vizceral
The Docker image also contains demo data based on Netflix's public cloud infrastructure:
docker run -e "RTPROP=-Dviz.demo=yes" -p 8008:8008 sflow/vizceral
In this case, the detailed view shows messages flowing between microservices running in the Amazon public cloud. Similar visibility could be obtained by deploying Host sFlow agents with associated modules for web and application servers and modifying sflow/vizceral to present the application transaction flows. In private data centers, sFlow support in load balancers  (F5, A10) provides visibility into interactions between application tiers. See Microservices for more information on using sFlow to instrument microservice architectures.
Collecting Docker Swarm service metrics describes how meta data about services running on Docker Swarm can be combined with sFlow telemetry to generate service level metrics. A similar approach could be taken to display Docker Swarm service interactions using Vizceral. Using network visibility to measure flows between services greatly simplifies the monitoring task, avoiding the challenge of adding instrumentation to each container.

Tuesday, September 5, 2017

Troubleshooting connectivity problems in leaf and spine fabrics

Introducing data center fabric, the next-generation Facebook data center network describes the benefits of moving to a leaf and spine network architecture. The diagram shows how the leaf and spine architecture creates many paths between each pair of hosts. Multiple paths increase available bandwidth and resilience against the loss of a link or a switch. While most networks don't have the scale requirements of Facebook, smaller scale leaf and spine designs deliver high bandwidth, low latency, networking to support cloud workloads (e.g. vSphere, OpenStack, Docker, Hadoop, etc.).

Unlike traditional hierarchical network designs, where a small number of links can be monitored to provide visibility, a leaf and spine network has no special links or switches where running CLI commands or attaching a probe would provide visibility. Even if it were possible to attach probes, the effective bandwidth of a leaf and spine network can be as high as a Petabit/second, well beyond the capabilities of current generation monitoring tools.

Fortunately, industry standard sFlow monitoring technology is built into the commodity switch hardware used to build leaf and spine networks. Enabling sFlow telemetry on all the switches in the network provides centralized, real-time, visibility into network traffic.
Fabric View describes an open source application running on the sFlow-RT real-time analytics engine. The Fabric View application provides an overview of the health of the entire leaf and spine fabric, tracking flows and counters on all links and summarizing information in a set of fabric level metrics and dashboards. In addition, Black hole detection describes how to detect routing anomalies in the fabric using the forwarding information included in the sFlow telemetry stream.

The sFlow sampling mechanism implemented in the switches is a highly scaleable method of passively collecting traffic information. However,  analyzing failed connections can be a challenge since very few packets are generated and the chance of sampling these packets is small. The traditional tools used to diagnose connectivity issues, ping and traceroute, are of limited value in a leaf and spine network since they only test a single path and are likely to miss the path that is experiencing difficulties.

An alternative method of addressing the multi-path tracing problem is to enable filtered packet capture on each switch, programming the filters to capture the packets of interest. However, this method can be slow and complex since every switch needs to be configured for each test and the switch configurations need to be cleared after the test has been completed.

This article explores how the hping3 tool can be used with sFlow to trace packet paths across the fabric and detect where they are being lost. The following Python script,, uses sFlow-RT's REST API to program a flow to watch for a specific flow and print the links that it traverses:
#!/usr/bin/env python
import argparse
import requests
import json
import signal
from random import randint

def sig_handler(signal,frame):
signal.signal(signal.SIGINT, sig_handler)

parser = argparse.ArgumentParser()
parser.add_argument('filter', help='sFlow-RT flow filter, e.g. "ipsource="')
args = parser.parse_args()

rt = 'http://localhost:8008'
name = 'trace' + str(randint(0,10000))

flow = {'keys':'link:inputifindex','value':'frames',

flowurl = rt+'/flows/json?maxFlows=100&timeout=60&name='+name
flowID = -1
while 1 == 1:
  r = requests.get(flowurl+'&flowID='+str(flowID))
  if r.status_code != 200: break
  flows = r.json()
  if len(flows) == 0: continue

  flowID = flows[0]["flowID"]
  for f in flows:
    print f['flowKeys']
Note: See RESTflow for a description of the sFlow-RT REST API.

First run the following Python script, supplying a filter to select the packets of interest:
./ 'ipsource='
Note: Identifying characteristics of failed connections may be inferable from application error logs. Otherwise, running packet capture on the affected host (tcpdump/wireshark) can identify the network attributes of interest.

Next, log into the host that is having connectivity problems and generate traffic matching the flow:
sudo hping3 -c 100000 -i u100 --udp -k -s 1111 -p 53
Note: The above command sends 100,000 packets at a rate of 1 packet every 100 microseconds (i.e. at a rate of 10,000 packets per second).  Select a packet rate that will not disturb production traffic on the network and make sure to send enough packets so that at least one packet will be sampled on each link. For example, for 10G links the packet sampling rate should be around 1-in-10,000 so generating 100,000 packets means that there is a 99.995% chance that a link carrying the flow will generate at least 1 sample (the probability is easily calculated using the Binomal distribution, see Wolfram Alpha).

The script will start printing links traversed by the flow immediately they are detected (typically in less than a second after starting the test):
./ 'ipsource='
The above example traced the single path traversed by a specific connection. To explore all paths, drop the source port and hping3 will cycle through source ports and the traffic should be visible on all the equal cost paths (provided that a layer 4 hash function has been selected by the switches).

Drop the source port from the filter:
./ 'ipsource='
Drop the -k and -s options from the hping3 command:
sudo hping3  -c 100000 -i u100 --udp -p 53
The open source trace-flow application is a graphical version of the script written using sFlow-RT's JavaScript API (see Writing Applications). The screen capture above displayed the path for the test traffic within a second of the start of test.

Continuous network-wide monitoring of leaf and spine networks using sFlow leverages the capabilities of commodity switch hardware and provides centralized visibility that simplifies network operation and trouble shooting.