|Snow flakes by Wilson Bentley|
The following table examines the approaches taken by the IPFIX and sFlow standards by contrasting how they handle four basic aspects of measurement.
Note: The IPFIX standard is based on Cisco's NetFlow™ version 9 protocol and most of the points of comparison apply equally to NetFlow.
|Packet||IPFIX currently defines over 50 fields relating to packet header (see IP Flow Information Export (IPFIX) Entities):
||The sFlow standard specifies a single way to report packet attributes, the packet header, ensuring that every vendor and product produces compatible results.|
Every sFlow compatible device deployed since the sFlow standard was published in 2001 provides visibility into every protocol that has ever, or will ever, run over Ethernet. The packet header includes all the protocol fields exported by IPFIX as well as fields associated with emerging protocols such as FCoE, AoE, TRILL, NVGRE and VxLAN that have yet to by defined in IPFIX.
|Time||IPFIX has over 30 elements that can be used to represent time (see IP Flow Information Export (IPFIX) Entities):
||The sFlow standard requires that data be sent immediately. The stateless nature of the protocol means that data can be combined and timestamps added by the central sFlow collector without any need for timestamps or time synchronization among the agents.|
Note: The sFlow datagrams do contain a time stamp, the agent uptime in milliseconds at the time the datagram was sent.
|Sampling||IPFIX currently defines eight different algorithms for packet sampling (see IANA Packet Sampling Parameters):||The sFlow standard mandates a single, statistically valid, sampling algorithm. All sFlow compliant vendors and products, implement the same algorithm and produce accurate, interoperable results.|
|URL||There is no-standard IPFIX element for exporting a URL. However, IPFIX does allow vendor extensions, resulting in multiple schemes for exporting URL data. Examples include:||The sFlow standard mandates a set of HTTP counters and transaction attributes that ensures consistent reporting from HTTP aware entities such as web servers (Apache, Tomcat, NGINX etc.) and load balancers (F5 etc.), irrespective of vendor or internal architecture.|
Each URL is exported as part of the standard transaction record that includes: client IP, server IP, referrer, authuser, user-agent, mime-type, status, request-bytes, response-bytes, response time. In addition, the sFlow standard defines a unified data model that links measurements from network devices, servers and application instances to provide a comprehensive, data center wide, view of performance.
From the examples in the table, it is apparent that IPFIX and sFlow standards take two very different approaches. The IPFIX standard is descriptive, defining a standard set of attributes that vendors can use to describe the information that they choose to export. The result is that vendors use IPFIX to differentiate each product, reporting a unique and inconsistent set of measurements based on its internal architecture and product features. In contrast, the sFlow standard is prescriptive, defining a set of measurements that every vendor must implement. While IPFIX provides a way to describe each "snowflake", the sFlow standard results from vendors working together to identifying common measurements and implement them in an interoperable way.
Henry Ford transformed the auto industry by moving from hand-made, custom parts to standardized components and processes that allowed for mass production. The data center is undergoing a similar transformation, from small, static, custom environments to large scale, commoditized, flexible, cloud architectures. The sFlow standard delivers the universal performance measurements needed for automation, enjoys broad vendor support, and along with other disruptive technologies like 10G Ethernet, merchant silicon, Software Defined Networking (SDN), OpenFlow, networked storage and virtualization is enabling this transformation.