NetFlow Monitoring

Overview

The NetFlow view in Network Device Monitoring provides visibility into network traffic flows collected from devices that export flow data (for example, routers, firewalls, or switches). You can analyze traffic volume, identify top talkers, and understand how data moves through your network.

The NetFlow view displays traffic metrics aggregated by device and interface. Use it to identify which devices or interfaces are consuming the most bandwidth, generating the most packets, or contributing to traffic spikes.

Side Navigation

Use the left-hand navigation to explore additional NetFlow views:

• Traffic Volume: Overall flow metrics by device and interface.
• Device Health: Status and utilization of monitored devices.
• Flows: Detailed individual flow records.
• Conversations: Aggregated source–destination pairs.
• Autonomous Systems: Flow data grouped by Autonomous System Numbers (ASNs).
• Geo IP: Flow data grouped by geographic origin/destination.
• Source Ports / Destination Ports / Protocols / Flags: Traffic breakdown by packet metadata.

Installation

To use NetFlow Monitoring with Network Device Monitoring, ensure you are using the Agent version 7.45 or newer.

Note: Configuring metric collection from Network Device Monitoring is not a requirement for sending NetFlow data, although it is strongly recommended as this extra data can be used to enrich your flow records with information such as the device name, model, and vendor, as well as the inbound/outbound interface name.

Configuration

To configure your devices to send NetFlow, jFlow, sFlow, or IPFIX traffic to the Agent NetFlow server, your devices must be configured to send traffic to the IP address that the Datadog Agent is installed on, specifically the flow_type and port.

1. Edit your datadog.yaml Agent configuration file to enable NetFlow:

network_devices:netflow:enabled:truelisteners:- flow_type: netflow9 # choices:netflow5, netflow9, ipfix, sflow5port:2055# devices need to be configured to the same port number- flow_type:netflow5port:2056- flow_type:ipfixport:4739- flow_type:sflow5port:6343## Set to true to enable reverse DNS enrichment of private source and destination IP addresses in NetFlow recordsreverse_dns_enrichment_enabled:false

2. After saving your changes, restart the Agent.

   Note: Ensure that your firewall rules allow incoming UDP traffic on the configured ports.

Aggregation

The Datadog Agent automatically aggregates the data received into NetFlow to limit the number of records sent to the platform while maintaining most of the information. By default, flow recordings that have the same identifiers, such as source, destination address, port, and protocol, are aggregated together in five minute intervals. Additionally, the Datadog Agent can detect ephemeral ports and remove them. As a result, you may see Flows with port:*.

Enrichment

Your NetFlow data is processed by the Datadog backend and enriched with the available metadata from your devices and interfaces. Enrichment is based on the NetFlow exporter IP and the interface indexes. To disambiguate possible collisions between reused private IPs, you can configure a different namespace for each Agent configuration file (with the setting network_devices.namespace).

If the NetFlow exporter IP is one of the device IPs, but not the one configured on the SNMP integration, Datadog attempts to locate the device that the exporter IP belongs to, and enriches your NetFlow data with it is as long as the match is unique.

Cloud provider IP enrichment

Datadog enriches IPs with public cloud provider service and region for IPv4 addresses, so you can filter for flow records from a specific service and region.

Port enrichment

Datadog enriches ports in NetFlow with IANA (Internet Assigned Numbers Authority) data to resolve well known port mappings (such as Postgres on 5432 and HTTPS on 443).

Custom port enrichment

You can also add your own custom enrichments to map ports and protocols to specific applications (for example, if a custom service runs on a specific port). This makes it easier for network engineers and their teams to interpret and query NetFlow data with human-readable names.

From the Configuration tab in NetFlow, click + Add Enrichment to upload the CSV file containing your custom enrichments.

Custom IP enrichment

You can also add your own custom enrichments to map IPs and CIDRs to custom tags (for example, to categorize services running on specific IP addresses). This makes it easier for network engineers and their teams to interpret and query NetFlow data with human-readable names.

From the Enrichment settings page, click + Add Enrichment to add mappings manually or upload a CSV file to add mappings in bulk.

Reverse DNS private IP enrichment

Enable Reverse DNS private IP enrichment to perform DNS lookups for hostnames associated with source or destination IP addresses. When enabled, the Agent conducts reverse DNS lookups on source and destination IPs within private address ranges, enriching NetFlow records with the corresponding hostnames.

By default, the Reverse DNS IP enrichment in your datadog.yaml file is disabled. To enable, see the Configuration section of this page.

Search for DNS in the + Filter menu to locate flows associated with Reverse DNS IP enrichment:

Note: Reverse DNS entries are cached and subject to rate limiting to minimize DNS queries and reduce the load on DNS servers. For more configuration options, including modifying default caching and rate limiting, see the full configuration file.

IP details

In the Conversations view, you can view the Public IP address of the Destination IP. Hover over the IP to display rich metadata about the IP and a link to View Related Network Connections where you can inspect the connectivity in more detail.

Flow diagram

You can visualize the flows in NetFlow Monitoring by clicking on the Flows menu and hovering over a flow from the list to view additional information about Source IP, Ingress Interface Name, Device name, and Destination IP across related network connections.

Network Path for NetFlow

Dynamic Tests for NetFlow can automatically run Network Path tests from the Agent that collects NetFlow traffic to destination IPs observed in NetFlow records. Use Dynamic Tests for NetFlow to add hop-by-hop route and latency context to your NetFlow destinations.

Dynamic Tests for NetFlow are experimental and require Agent v7.81+. To set up Dynamic Tests for NetFlow, see Network Path setup.

NetFlow monitor

Click on the Create Monitor icon from any of the views to create a NetFlow monitor. When creating the monitor, consider the following fields with respect to the source IP or destination IP from the perspective of the device. These fields provide insights into network traffic patterns and help with optimizing performance and security.

Interface information

The following fields represent details about the ingress and egress interfaces.

Device information

The following fields represent details related to the device generating NetFlow records.

Flow details

The following fields represent characteristics of the network flow.

In addition to fields, you can also use out-of-the-box facets to start analyzing traffic patterns based on NetFlow destination and source IP addresses.

NetFlow Destination IP facets

NetFlow Source IP facets

Conversation stitching

By default, NetFlow records separate unidirectional flows for each direction of traffic between two endpoints (A → B and B → A). Conversation stitching combines these into a single bidirectional record, giving you a complete view of the total traffic exchanged between two endpoints (A ↔ B).

With conversation stitching, you can:

• See total traffic exchanged between two endpoints as one conversation instead of separate directional flows
• Identify true initiators and responders so that source and destination widgets reflect accurate roles
• Remove noise where servers incorrectly appear as top sources

To toggle between stitched (bidirectional) and unstitched (unidirectional) views, navigate to any endpoint-based NetFlow view and use the Bidirectional toggle under the time picker.

Sampling rate

NetFlow’s sampling rate is taken into account in the computation of bytes and packets by default. The displayed values for bytes and packets are computed with the sampling rate applied. Additionally, you can query for Bytes (Adjusted) (@adjusted_bytes) and Packets (Adjusted) (@adjusted_packets) in dashboards and notebooks to visualize them.

To visualize the raw bytes/packets (sampled) sent by your devices, you can query for Bytes (Sampled) (@bytes) and Packets (Sampled) (@packets) in dashboards and notebooks.

Retention

NetFlow data is retained for 30 days by default, with options for 15, 30, 60, and 90 day retention.

Limit flow volume per flush interval

To control NetFlow volume and associated costs, configure the Agent to cap the number of flow records submitted per flush interval. The flush interval is the period during which flows are aggregated before being forwarded to Datadog.

When this limit is enabled, the Agent retains only the top flows by byte count up to the configured maximum, and drops lower-volume flows for that flush interval.

Configuration

Note: Requires Agent version 7.75.1 or later.

Configure the following in your datadog.yaml:

network_devices:netflow:enabled:trueaggregator_max_flows_per_flush_interval:10000

With this configuration, the Agent submits at most 10,000 NetFlow records per flush interval (5 minutes by default). The Agent prioritizes the highest-volume flows and drops the rest.

Estimating daily volume

Your approximate daily maximum flow count is:

max_flows_per_flush_interval * (minutes_per_day / flush_interval_minutes)

For example, with 10,000 flows per flush and a 5-minute flush interval:

10,000 * (1440 / 5) = 2,880,000 flows/day

Expected behavior

• Top talkers are prioritized: This is best for workflows focused on high-volume traffic (for example, bandwidth drivers and noisy links).
• Reduced visibility for low-volume flows: Lower-traffic source/destination pairs may not appear when the cap is reached.
• Per-Agent behavior: The limit is enforced on each Agent independently. If multiple Agents see traffic for the same conversations, they are not globally aggregated before truncation.

Monitoring truncation

When flow limiting is enabled, the Agent emits metrics you can use to understand how much data is being kept versus dropped:

• ndm.flow_truncation.flows_total
• ndm.flow_truncation.flows_kept
• ndm.flow_truncation.flows_dropped
• ndm.flow_truncation.keep_ratio
• ndm.flow_truncation.threshold_value
• ndm.flow_truncation.runtime_ms

Use these metrics to validate your chosen cap and to detect when truncation is occurring frequently (which may indicate you should adjust the cap or the flush interval).

Troubleshooting

NetFlow packet drops

NetFlow packet drops can occur when there are a high number of NetFlow packets per second, typically greater than 50,000. The following steps can help identify and mitigate NetFlow packet drops:

Identifying packet drops

Use the netstat -s command to see if there are any dropped UDP packets:

 netstat -s

Mitigation steps

1. Increase the Number of NetFlow Listeners

Increase the number of NetFlow listeners by using a configuration similar to the following: Datadog recommends setting the number of workers to match the number of CPU cores in your system:

netflow:enabled:truelisteners:- flow_type:netflow9port:2055workers:4# 4 CPUs

2. Increase UDP Queue Length (Linux only)

Adjusting your system’s UDP queue length can help accommodate the higher volume of NetFlow packets. Increase the UDP receive buffer size to 25MB by executing the following commands:

 sudo sysctl -w net.core.rmem_max=26214400
 sudo sysctl -w net.core.rmem_default=26214400

3. Persisting the configuration (Linux only)

To make these changes permanent, add the following lines to your /etc/sysctl.conf file:

 net.core.rmem_max=26214400
 net.core.rmem_default=26214400

Further Reading

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