9.3. Threshold crossing alerts (TCAs)

You can assign thresholds to any meter value. Trisul continuously monitors the value of the traffic meter against the configured thresholds and generates a “Threshold Crossing Alert” if the value crosses the thresholds.


You can monitor a single Key or a Key Range. Some examples:

  1. monitor DNS Port-53 traffic and raise an alert if it crosses 50kbps for 3 minutes
  2. monitor IP Address if it crosses 10Mbps for 5 minutes raise alert then CLEAR if it dips below 5 Mbps
  3. monitor IP Range to raise alert if ANY IP in that range crosses 1 Gbps for 1 minute

9.3.1 High and Low Watermarks for alerts

The two knobs you use are Watermarks and Sustained Intervals.

You assign Hi-Water and Lo-Water marks to the meter value you want to keep an eye on. When the meter value crosses the Hi-Water mark it is treated as a FIRED event and when it crosses the Lo-Water mark, it is treated as a CLEAR event.
Sustained Intervals
To prevent flapping of alerts due to meter value fluctuating around the watermarks, you can also specify a number called Sustained Interval. If you specify a sustained interval of 3, then the meter value has to be above or below the high and low watermarks respectively for 3 consecutive time bucket intervals (by default 60 seconds) before the corresponding FIRE or CLEAR alert is fired. The Low Watermark is optional.

The following picture illustrates this. Here we are setting up a TCA for :

  • If value of meter exceeds 100Kbps for 3 consecutive intervals – we FIRE a TCA
  • If value of meter drops less than 80Kbps for 2 consecutive intervals – we CLEAR a TCA

Threshold Crossing Alerts showing FIRE and CLEAR conditions

Note that :

  • The TCA does not fire in the zone between HI and LO water marks
  • The TCA fires only once even when multiple consecutive values are over the HI water mark
  • For a TCA to fire again, the values have to dip below the LO water mark and re-cross the HI water threshold again

9.3.2 Configuring

Creating a new TCA based on Counter group

Select Alerts → Threshold Crossing Alerts → Configure TCA
  1. Click New Threshold Crossing Alerts , which leads to the page whose fields are described below
FieldName Optional Description
Name of the alert A name for this alert, this will show up on screen and reports
Target counter group Select the target counter group from the dropdown
Target Key or Range The key or key range within the target counter group on which you want to create a TCA. You may enter a single key or a key range

Single key
You can enter this in either human readable format eg:Port-80, or in Trisul key format: p-0050, C0.A8.00.01
Key range
Enter the first and last key in the range inclusive using a tilde ~ or to. Example IP range : ~ or port range (1 to 1024) 1 to 1024 using the to keyword
Target Metric Meter within the counter group
Hi Water Mark High threshold mark. Eg: 10Mbps, 6Kbps, 2000. Default units = bytes/sec so if you just say 10M it would be interpreted as 10Mbps depending on the meter selected
Hi Water Sustained Intervals TCA triggered if over Hi Water for this many intervals
Lo Water Mark optional Low threshold mark
Lo Water Sustained Intervals optional TCA cleared if below Lo Water for this many intervals
TCA Message When the TCA fires or clears, this message is emitted. You can see this message on Trisul UI modules and on email alerts

9.3.3 Example DNS TCA

This example creates a TCA when DNS traffic crosses 1.2Mbps for 2 minutes and clears when it drops below 600Kbps

FieldName Input
Name DNS over 1.2Mbps
Target Apps
TargetKey Port-53 , 53, or domain or in Trisul Internal Key format p-0035
Stat ID Total
Hi Water Mark 1.2Mbps
Hi Water Sustained Intervals 2
Lo Water Mark 600Kbps
Lo Water Sustained Intervals 1
TCA Message DNS traffic is double of expected at 1.2Mbps, action required team !

9.3.4 Viewing TCAs

There are many methods to view, search and export TCAs.

Select Alerts → Threshold Crossing Alerts
  1. You will now see a table listing all the alerts grouped by alert type and count
  2. Clicking on the number seen under the Count column of an alert takes you to a more detailed view of the alerts

Showing counts of alerts generated for each TCA type

Viewing individual alerts

Clicking on alert count on a TCA will take you to the alerts view.

Showing list of fired and cleared alerts

You can see the search form in this page

  1. To query for specific alerts enter the time window and a regex to search for alerts with message matching a certain pattern. For example enter an IP address to pick all alerts from that IP address.


When alerts are displayed you have the option to drilldown even further.

  1. press the tag button to bring up drilldown options similar to those found on other dashboards (see image)
  2. press the chart button to show a traffic chart around the time the alert occurred showing the Low and High water marks for reference.

TCA drilldown options and traffic charts showing the alert traffic

Exporting to PDF, CSV, Excel

When a table shows list of alerts
  1. Locate the Download button above the table
  2. Select “Download PDF”, “Download CSV” or “Download XLSX” options

This allows you to export and share displayed alerts

Alerts dashboard

  • Add the Threshold Crossing Alert module to any dashboard

This module auto updates itself as new TCAs are generated. You can add this module to any dashboard position.

How to add modules to dashboard

9.3.5 Deleting TCAs

The default approach of Trisul is not to delete anything. TCAs just rollover as they age out. Yet if you wish to explicitly delete TCAs you can use the following steps :

Select Alerts → Threshold Crossing Alerts
  1. Click the Delete all icon under each TCA to delete it
This deletes all the alerts fired under that TCA , but not the TCA itself

9.3.6 Automatically emailing TCAs

There are two types of email reports you can use for notifying these TCA alerts.

TCA Email Alerts intelligently pull up the following relevant pieces of information and include them in the email. Top Hosts, Top Apps, Top Flows, and Top Conversations related to the alert.

Intelligent TCA Email reports for routers interfaces

A commonly used TCA is on Netflow mode routers and interfaces. When a TCA is created on such an interface the following information is automatically included in the alert email.

  1. Top applications on that interface which alerted
  2. Top hosts
  3. Top conversations.

This allows the receiver of the email to immediately spot the source of the alert without even logging on to Trisul Network Analytics.

Enabling inteface tracking allows for richer TCA alerts. See Netflow Interface Trackers

Real time email

Configure Email Alerting for real time alerts.

Periodic email digest

You can schedule a Threshold Crossing Alert report which will automatically email you a list of TCAs that fired on a hourly or daily basis.

  1. A single consolidated email is sent out containing details of all TCAs
  2. No email is sent out if there are no TCAs to report

9.3.7 Bulk configuration

We can also configure TCAs for one or more interfaces from a particular router in bulk rather the one by one.

You can throw an alert if the Interface crosses 200 Mbps.

Login as Admin. Select Context : default → profile0 → Netflow Wizard → Interfaces

You can select one or more interfaces from a router and Click on Configure TCA option to create an alert.

Field Name Description
Interfaces Key for Interface
Meter Total,in or out
Hi Water Mark Hi Threshold Mark
Hi Water Sustained Intervals TCA Fired only if metric values is over Hi Water for this many minutes
Lo Water Mark Low Threshold Mark
Lo Water Sustained Mark TCA Cleared only if metric value is below Lo Water for this many minutes
TCA Message A custom message that appears when these alerts fire