Monday, December 22, 2014

Fabric visibility with Cumulus Linux

A leaf and spine fabric is challenging to monitor. The fabric spreads traffic across all the switches and links in order to maximize bandwidth. 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.

The 2 minute video provides an overview of some of the performance challenges with leaf and spine fabrics and demonstrates Fabric View - a monitoring solution that leverages industry standard sFlow instrumentation in commodity data center switches to provide real-time visibility into fabric performance.

Fabric View is free to try, just register at and request an evaluation. The software requires an accurate network topology in order to characterize performance and this article will describe how to obtain the topology from a Cumulus Networks fabric.

Complex Topology and Wiring Validation in Data Centers describes how Cumulus Networks' prescriptive topology manager (PTM) provides a simple method of verifying and enforcing correct wiring topologies. The following script converts the topology from PTM's dot notation to the JSON representation used by Fabric View:
#!/usr/bin/env python

import sys, re, fileinput, requests, json

url = sys.argv[1]
top = {'links':{}}

def dequote(s):
  if (s[0] == s[-1]) and s.startswith(("'", '"')):
    return s[1:-1]
  return s

l = 1
for line in fileinput.input(sys.argv[2:]):
  link ='([\S]+):(\S+)\s*(--|->)\s*(\S+):([^\s;,]+)',line)
  if link:
    s1 = dequote(
    p1 = dequote(
    s2 = dequote(
    p2 = dequote(
    linkname = 'L%d' % (l)
    l += 1
    top['links'][linkname] = {'node1':s1,'port1':p1,'node2':s2,'port2':p2}

The following example demonstrates how to use the script,converting the file to JSON and posting the result to the Fabric View server running on host fabricview:
./ http://fabricview:8008/script/fabric-view.js/topology/json
Cumulus Networks, sFlow and data center automation describes how enable sFlow on Cumulus Linux. Configure all the switches in the leaf and spine fabric to send sFlow to the Fabric View server and you should immediately start to see data through the web interface, http://fabricview:8008/. The video provides a quick walkthrough of the software features.

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