General Metrics

The general metrics used in Kentik queries are discussed in the following topics:

• About General Metrics
• Metrics from All Devices
• Host Traffic Metrics
• Application Decodes Metrics

Notes:
- The categorization of metrics in the topics below corresponds to the categories by which they are grouped in the Metrics dialog (see Metrics Dialog UI).
- For general information about metrics in Kentik, see About Metrics.
- For metrics that aren't transmitted via a flow protocol, see Non-flow Metrics.
- For metrics that are device-specific, see Device-specific Metrics.
- Metrics that are available as filter or group-by dimensions are covered in the KB's Dimensions Reference (see Per-flow Metrics).
- In addition to being used for query settings in the Kentik portal, metrics are also used for the Query API.

In Kentik, general metrics are those transmitted via flow protocols like NetFlow or sFlow. They are not tied to specific devices, such as particular router models. The availability of these metrics in settings like the Metrics Pane of the Query sidebar in Data Explorer depends on the device category (Router or Host) and the specific device type (see Supported Device Types).

When a query includes traffic solely from data sources (see About Data Sources) in the "Routers" category, only the following metrics are available:

Notes:
- The “Total” metric is available only when the chart type is set to Table or Matrix (see Chart View Types).
- Metrics labeled as "unique" are evaluated across all instances on queried devices within each individual time slice of the query's time range, but not between different time slices (see Table Time-slicing).

When querying traffic that includes devices in the "Host" category (using Kentik’s host agent, see About the Universal Agent), the data from these hosts is stored in KDE. This enables host-only metrics, which are detailed in the following topics:

• Host Metrics by Protocol
• Host Metrics Descriptions
• Host Metrics KDE Columns

As shown in the table below, the availability of a given metric varies depending on the protocol:

Note: The “Total” metric is available only when the chart type is set to Table or Matrix (see Chart View Types).

The following descriptions apply to the host-only metrics listed in the table above:

• Retransmits: Packets re-sent from source to destination, applicable to reliable protocols like TCP. Indicates network delivery issues affecting performance. Measured per second and as a percentage of all packets sent.
  Note: "Repeated" refers to packets retransmitted 3 or more times.
• Out of order: Packets arriving out of sequence. High values suggest variability in delivery paths, impacting latency-sensitive traffic like real-time audio/video. Measured per second and as a percentage of all packets sent.
• Fragments/second: Packets split into smaller packets for network delivery. Fragmentation can increase CPU load and cause retransmits if fragments arrive out-of-order. Measured per second and as a percentage of all packets sent.
• Zero Windows: Count of TCP receive windows with a value of zero, indicating a full buffer.
• Receive Window: Size of the TCP receive window.
• Latency: Various measures include:
  - RTT/2 client latency (derived): One-way latency from the client perspective. High values indicate network or server-side issues.
  - RTT/2 server latency (derived): One-way latency from the server perspective. High values indicate network or client-side issues.
  - RTT/2 application latency (derived): Derived from request/response pairs at the application layer, indicating end-user experience latency. Effective for protocols with clear request/response pairings.
  - First Payload Exchange Latency: Measures application response time when the protocol isn't understood or can’t be decoded (e.g., HTTPS, SQL). Excludes TCP setup, starting with the first packet sent and ending with the first packet returned.

The following table shows the correspondence between the metrics described above and the columns of the Kentik Data Engine (KDE):

When using Kentik's software host agent for application decodes (see About Application Decodes), both dimensions and metrics are generated and stored in or derived from KDE columns. The metrics available for queries via the metric selector (see Metrics Dialog UI) include:

Note: For dimensions related to application decodes, see Application Decodes Dimensions.

The "legacy" metrics in the table below are from older versions (<v1.3.0) of Kentik’s legacy host software agent, kprobe: